Plant Secondary Metabolites UPDATES

Acai Berries —

love of all things antioxidant.

While it is difficult to be against antioxidants, I have to say I am not impressed. Oxidation is a normal end-product of metabolism and is required to kill bacteria and, probably tumor cells, within white blood cells. So if you’re not worried about infections or cancer, antioxidants are pretty good. I feel the anti-oxidant story is hugely speculative. Think of all the care and attention goes into clinical trials to develop the efficacy of drugs and the beautiful experiments on the major nutrients, vitamins and elements. All we have with antioxidants is conjecture.

Juice and dried fruits contain a mix of oxidized and unoxidized antioxidants but there is no way of knowing how much in each state. This relates to the argument that any antioxidant can also serve as a pro-oxidant, given the proper conditions. There are both water soluble and water insoluble antioxidants and we don’t know how important aqueous versus lipid solubility is for a health benefit.

There haven’t been any convincing studies with antioxidant supplements (mostly vitamin E) to prevent heart disease and it is likely the small benefit seen in some studies (on heart disease only, not on mortality) is due to the anti-coagulant effect of tocopherol. In fact, some studies clearly show harm in patients taking statins and antioxidants.

It is the whole diet, sufficient in its details that matters and is sustainable.

Auxins and Receptor —

Thee is a constancy in protein structure throughout biology and also small MW molecules influence their biological activity. A major protein , small molecular weight interaction occurs at receptors.

I have long felt that the hormones that are active in the other Kingdoms e.g. plants may well have import in man. Obvious, so obvious examples are the vitamins and trace elements.

A very important plant hormone is auxin. This is produced in regions of actively dividing and enlarging cells that regulate plant growth. The action is to modulate gene expression and hence cell division, elongation and differentiation. The auxins include 3-acetic acid and indole-3-acetonitrile.

Their importance is shown by their availability in every Plant Nursery Shop or Garden Centre for rooting.

How the auxin works is still being studied.

Auxin is recognised by a small family of F-box proteins including transport inhibitor response 1 (TIR1. Auxin regulates gene expression by promoting SCF ubiquitin-ligase-catalysed degradation of the Aux/I AA transcription repressors, but how the TIR1 F-box protein senses and becomes activated by auxin remains unclear. In a recent paper in Nature crystal structures of the Arabidopsis TIR1-ASK1 complex show that the leucine-rich repeat domain of TIR1 contains an unexpected inositol hexakisphosphate co-factor and recognizes auxin and the Aux/I AA polypeptide substrate through a single surface pocket. Anchored to the base of the TIR1 pocket, auxin binds to a partially favourable site, which can also accommodate various auxin analogues. Docked on top of auxin, the Aux/IAA substrate peptide occupies the rest of the TIR1 pocket and completely encloses the hormone-binding site. By filling in a hydrophobic cavity at the protein interface, auxin enhances the TIRI-substrate interactions by acting as a ‘molecular glue’.

In plants, multiple phytohormone signalling pathways are now known to be regulated by ubiquitin ligases. In particular, jasmonic acid signalling requires COI1, an F-box protein with high sequence similarity to TIRT. It is feasible that COIl adopts a TIRl-like structure and possibly functions as a jasmonic acid receptor. Most of the auxin-contacting residues in T1RI are indeed not conserved in COI1. Although TIRI orthologues, so far are only found in plants, a small ligand-sensing site regulating substrate recruitment could conceivably be evolved in a different structural context in other human ubiquitin ligases.

An increasing number of human disorders has now been associated with defective ubiquitin-ligase-substrate interactions owing to mutations of the ligases themselves, ubiquitination substrates or upstream signalling proteins responsible for substrate priming. The regulator.’ mechanism of TIKI by auxin suggests that it is possible for small molecules to promote protein-protein interactions in ubiquitin ligases. and potentially other protein interaction systems that arc impaired by genetic alterations.

When we eat plants and presumably ingest auxins do these compounds play a necessary par in our metabolism. A wonderful research project

Tan et al 2007 Nature April 5th vol 446, pp 640-644
Guilfoyle 2007 Nature April 5th vol 446 pp 621-2

Plant Secondary Metabolites —

Bonepolyphenols —

In Nutrition Research Review 2007 , 20, 89-105, T. P. al write on Bone mineral density, polyphenols and caffeine: a reassessment

In an ageing society, the maintenance of good bone health with age is important. In osteoporosis, bone becomes increasingly porous, resulting in both greater chance and severity of bone fracture at the hip. spine, forearm and shoulder. Bone fractures result in reduced mobility, discomfort and a higher risk of early mortality. Osteoporosis can cost the UK over £1-7 billion for the treatment of hip fracture.

Elderly women are at risk from osteoporosis, because they can lose between 10 and 15 % of their bone every decade after the menopause. Women lend to have lower peak bone mass than men, and that levels of oestrogen (a hormone with a positive effect on bone health) are decreased during and after menopause and tend to live longer than men.

Bone tissue is in a constant state of flux. The skeleton has obvious mechanical roles and is also a Calcium depository for the rest of the body, with calcium being removed and replaced as required. The state of bone flux within an individual can be described in terms of bone mineral density. Bone metabolism is controlled by a variety of growth hormones, sex steroid hormones (such as oestrogens), thyroxine. corticosteroids and insulin. Three hormones play vital roles, 1.25-dihydroxycholecalciferol. parathyroid hormone and calcitonin. As well as affecting dietary calcium adsorption efficiencies, these hormones also influence the three cell types relevant to bone formation and metabolism osteoblasts (hone formation), osteocytes (bone maintenance) and osteoclasts (bone resorption). The balance between the formation and resorption of bone tissue is affected by genetic and environmental (for example, diet and lifestyle) factors.

Several studies have shown benefit from drinking tea and bone mineral density and fracture risk. This could be due to the fluoride and polyphenol components of tea. Caffeine consumption has been sen as a potential risk factor for low bone mass density and high fracture risk.

Fruit and vegetable intake which includes increased polyphenols intake may also contribute positively to bone health.

In this review the evidence surrounding the function(s) of poly phenol-rich foods in bone health is examined, along with more recent studies challenging the relevance of caffeine consumption to in vivo Ca balance. Plant foods rich in polyphenols such as tea. fruit and vegetables, as significant factors in a healthy diet and lifestyle, may have positive rules in bone health, and the negative role of caffeine may have been overestimated.

Cranberry —

This review by Pappas and Schaich discusses Vaccinium macrocarpon, the American cranberry, recording a comprehensive list of phytochemical components, and their prevalence in cranberry fruit and its products. Increased dietary consumption of fruits and vegetables may improve increased cardiovascular health and may reduced the risk of cancer, stroke, degenerative diseases, loss of functionality associated with aging, and more. While fruits and vegetables are rich sources of vitamins and minerals, recent attention has focused on the effects of other chemicals present in fruit and vegetables , phytochemical components such as flavonoids, stilbenes, nonnutritive carotenoids, phytoestrogens, terpenes and other di¬verse phenolics

The possible mechanisms of phytochemical action remain largely unexplained and are the subject of speculation and research. Antioxidant mechanisms have been proposed, especially for cardiovascular health, cancer and age-related degenerative diseases. Phytochemical interact with vital proteins, signal transduction pathways, and bind to pathogen. There is increasing signs that non-nutrient phytochemicals have a place in the health promotion afforded by fruits and vegetables.

Cranberries contain an abundance of flavonoids, especially colored anthocyanins, abundant flavonols, and unique proanthocyanidins, other notable active components include phenolic acids, benzoates, hydroxycinnamic acids, terpenes and organic acids. The health effects of cranberries, cranberry products, and isolated cranberry components in humans and animals, as well as in vitro, are discussed.

Finally, the effects of processing and storage on cranberry phytochemicals is discussed, with afocus on identifying research gaps and novel means to preserve their natural, health-promoting components.

Keywords anthocyanins, proanthocyanidins, flavonols, pheno\s, urinary tract infections, cancer, inflammation, absorption

( 2009 ) Phytochemicals of Cranberries and Cranberry Products: Characterization, Potential Health Effects, and Processing Stability. Critical Reviews in Food Science and Nutrition vol 49,741-781

Dri Polyphenols —

Gary Williamson * and Birgit Hoist

Dietary reference intake (DRI) value for dietary poly phenols: are we heading in the right direction?

Polyphenols are widely distributed in plant foods, and have been linked to improved human health through reduced risk of chronic diseases, especially cardiovascular. Although they do not cause classical deficiencies, recently they have been discussed as ‘lifespan essentials because they are needed to achieve a full lifespan by reducing the risk of a range of chronic diseases. A recent meta analysis shows promising actions of polyphenols from cocoa, soya and tea on flow mediated dilation, blood pressure and LDL cholesterol. Many epidemiological studies support the action of polyphenols or polyphenol-rich foods on health, but there are still many gaps in our knowledge. More adequately powered, randomised, placebo controlled human studies are needed on polyphenols. There is a large number of structurally different polyphenols which are relevant for health, and obtaining enough information to set a DRI for each of these will not be feasible in the foreseeable future. A new approach is needed, and a new way of thinking, which would apply not only to polyphenols but also to other phytochemicals. Today, a target intake value of polyphenols as ‘lifespan essentials’ needs to be based on the amount of polyphenols in ‘5-a-day’. We are heading in the right direction towards a DRI, but bioavailability and dose-effects, including toxic levels, need to be established before DRIs can be considered.

Williamson and Hoist 2008 Dietary reference intake (DRI) value for dietary polyphenols : are we heading in the right direction? British Journal of Nutrition 99 suppl 3 S 555-S58

Flavonoids and immunity —

Epidemiological evidence suggests that a high intake of plant foods is associated with lower risk of chronic diseases.

The mechanism of action and the components involved in this effect have not been clearly identified.

A class of secondary metabolites present in a wide range of plant foods: the flavonoids, have different biological roles.

The anti-inflammatory actions of flavonoids in vitro or in cellular models involve the inhibition of the synthesis and activities of different pro-inflammatory mediators such as eicosanoids, cytokines, adhesion molecules and C-reactive protein.

Molecular activities of flavonoids include inhibition of transcription factors such as NF-KB and activating protein-I (AP-l), as well as activation of nuclear factor-erythroid 2-related factor 2 (Nrf2).

In vitro evidence of activity is limited as non-physiological concentrations are used and in vivo flavonoids are extensively metabolized to molecules with different chemical structures and activities compared with the ones originally present in the food.

Human studies investigating the effect of flavonoids on markers of inflammation are insufficient, and are mainly focused on flavonoid-rich foods but not on pure molecules. Most of the studies lack assessment of flavonoid absorption or fail to associate an effect on inflammation with a change in circulating levels of flavonoids.

Human trials with appropriate placebo and pure flavonoid molecules are needed to clarify if flavonoids represent ancillary ingredients or key molecules involved in the anti-inflammatory properties of plant foods.

Serafini 2010 Antioxidants and the immune system Flavonoids as anti-inflammatory agents Proceedings of Nutrition Society vol 69 273-78

Garlic —

This is a very interesting paper in Critical Reviews in Food Science and Nutrition 2009 on the merit of garlic in the diet.

Natural plant products have a real place in combating various physiological threats including oxidative stress, cardiovascular problems, cancer, and immune dysfunction.

Garlic (Allium sativum} holds a unique position in history and was recognized for its therapeutic potential. Recent advancements in the field of immunonutrition, physiology, and pharmacology have emphasised its importance as a functional food against various pathologies. Extensive research work has been. carried out on the health promoting properties of garlic, often referred to its sulfur containing metabolites i.e. allicin and its derivatives.


Diallyl sulfide, Diallyl disulfide Diallyl trisulfide AllylMethyl sulfide AllylMethyl disulfide Allylmethyl trisulfide 2-vinyl-4H-I,3-dithiin


E- Ajoene , Z-Ajoene



Garlic has many modes of preparation which are believed to be effective against health risks and even used as dietary supplements such as age garlic extract (AGE) and garlic oil etc. Its components/formulations can scavenge free radicals and protect membranes from damage and maintains cell integrity. It also provides cardiovascular protection by lowering of cholesterol, blood pressure, anti-platelet activities, and thromboxane formation thus providing protection against atherosclerosis and associated disorders. Besides this, it possesses antimutagenic and antiproliferative properties that are interesting in chemoprevenrive interventions. Several mechanisms have been reviewed in this context like activation of detoxification phase-I and JJ enzymes, reactive oxygen species (ROS) generation, and reducing DNA damage etc. Garlic could be useful in preventing the suppression of immune response associated with increased risk of malignancy as it stimulates the proliferation of lymphocytes, macrophage phagocytosis, stimulates the release of interleukin-Z, tumor necrosis factor-alpha and interferon-gamma, and enhances natural killer cells.

Masood Sadiq Butt et al 2009 Garlic : Nature’s protection against physiological threats, Critcal Reviews in Food Science and Nutrition vol 49, pp 538-5551

Keywords Garlic, aged garlic extract, oxidative tress. hype cholesterolemia, malignancies, immunonutrition

Gherlin —

UCP2 mediates ghrelin’s action on NPY/ AgRP neurons by lowering free radicals

Zane B. Andrews et al 2008 Nature vol 454 pp 846-851

The gut-derived hormone ghrelin actson the brain by regulating neuronal activity

Ghrelin is a hormone with widespread activity. This paper links its activity with appetite control in a complex action involving fatty acids as a hypothalamic fuel and also carbohydrate and energy intake. Anti oxidant status also has a role. No doubt in time this will become clearer.

Ghrelin-induced feeding behaviour is controlled by arcuate nucleus neurons that co-express neuropeptide Y and agouti-related protein (NPY/AgRP neurons). The authors show that ghrelin initiates changes in hypothalamic mitochondria! respiration in mice that are dependent on uncoupling protein 2 (UCP2). Activation of this mitochondrial mechanism is critical for ghrelin-induced mitochondrial proliferation and electric activation of NPY/AgRP neurons for ghrelin-induced food intake. The UCP2-dependent action of ghrelin on NPY/AgRP neurons is driven by a hypothalamic fatty acid oxidation pathway involving AMPK, CPT1 and free radicals that are scavenged by UCP2.

Grapes —

White and red grapes

The wild grape is red. During the domestication of the grape a white cultivar developed. This may have occurred 3,000 or so years age. In 2005 Japanese scientists showed that this colour change occurred because of a mutation in the VvMYBA1 gene. This difference is consistent over the whole grape range, between red and white grapes. The gene controls the production of the red colour anthocyanin. This colour is also found in apples, strawberries, purple cabbage and blueberries

More recently Mandy Walker and her colleagues in the Commonwealth Research Organisation in Australia showed two genes along side each other which control anthocyanin production. Both must be mutated in the white grape.

This suggests that all the white grapes have a common ancestor. Seeds of white grapes have been fond in the tomb of the Egyptian King Tutankamen ( 1322 BC ). So the mutation antedates this.

This was reviewed by Stephen Pincock in FT magazine March 31 p 11.

Honey, Yoghurt —

Honey, yoghurt and Runniness

When one of my children was young he would lean back after eating delicious honey laden yoghurt and say ” I love the way that trickles down my tummy” Very satisfying.

What happens and the the mechanism is not one that is highlighted in Nutrition

Even the simplest ingredients can give rise to complex patterns. Mark Buchanan of the University of Oslo, Norway, and his team have tackled one family of patterns — those formed when fluids containing suspended particles flow down a vertical surface. Langmuir 23,3732-3736 (2007)

Yoghurt running down the side of a pot, for example, is cut through by vertical, branched channels, whereas honey tends to break up into wavy horizontal bands. The particle size determines which type of pattern is produced.

Smaller particles leave behind vertical channels, because the downward flow of the film becomes focused along certain paths by a feedback mechanism that amplifies flow rate. Wavy horizontal bands appear in suspensions of larger particles, as particles get trapped by random imperfections on the vertical surface and jam together to form stress bearing arches.

So I love the way that trickles down my tummy. Very satisfying.

Taken from Nature 2007, vol 446, p 587

Isoflavone and Bone —

Ma and colleagues looked at studies of the effects of isoflavone intake on bone resorption and bone formation with a meta-analysis, of randomized controlled trials using urinary deoxypyridinoline, a bone resorption marker) and serum bone-specific alkaline phosphatase, a bone formation marker)

Nine studies with a total of 432 subjects were selected for meta-analysis. The urinary deoxypyridinoline concentration in subjects who consumed isoflavones decreased significantly. in comparison with that in subjects who did not consume isoflavones.

They concluded that soy soflavone intervention significantly inhibits bone resorption and stimulates bone formation in menopausal women:. These favorable effects occur even if less than 90mg/day of isoflavones are consumed or the intervention lasts less than 12 weeks.

Ma et al ( 2008)Soy isoflavone intake inhibits bone resorption and stimulates bone formation in menopausal women: meta-analysis of randomized controlled trials. European Journal of Clinical Nutrition 62, 155–161;

soy, isoflavone, osteoporosis, bone metabolism, deoxypyridinoline, bone-specific alkaline phosphatase

Isoflavones —

Isoflavones and their similarity to oestrogens., structurally and functionally

Isoflavones are plant chemicals which belong to the family of phyto-oestrogens. There are of interest to nutrition and health due to their potential oestrogenic properties in the body. There is close structural relationship of genistein and daidzein compared with 17ß-oestrodiol. Although oestrogenicity assays have reported low oestrogenic potency for dietary isoflavones (100-1000 times less than I7p-oestradiol;. However when dietary intakes of isoflavones are high their circulating concentrations could exceed endogenous oestradiol concentrations by up to 10000-fold which suggests potential physiological effects.

Isoflavones predominantly occur in plants as the water-soluble ß-glucosides, genistin. daidzin, glycitin which are hydrolysed by intestinal and bacterial ß-glucosidases. Genistein, daidzein and glycitein may be absorbed or further metabolised by gut microflora enzymes to isoflavone metabolites such as equol, dihydrogenistein. dihydrodaidzein, 6′-hydroxy-O-desmethylangolensin and -O-des-methylangolensin before absorption.

There is substantial evidence that oestrogen has beneficial effects on the cardiovascular system by enhancing NO production and thereby maintaining normal endothelial vasodilatory response and integrity of the vascular system. Oestrogen-like compounds such as isoflavones are also suggested to protect the endothelium and therefore be protective against the development of CVD.

Oestrogen-induced NO release occurs by more than one pathway. Oestrogen can act through the classical oestrogen receptor (ER)-transcriptional pathway, whereby eNOS gene expression is increased and NO production increases over hours or days. The ‘genomic’ effects of oestrogen. However, the acute effects, which are rapid in response and short in duration, may involve ERa-mediated activation of none-transcriptional pathways (non-genomic), or by a direct activation of cell-signalling pathways.

Oestrogen also appears to increase NO availability by modulating reactive oxygen species (ROS) and antioxidant status within the endothelial cell. Oestrogen has been shown to inhibit the production of NADPH oxidase and superoxide, attenuating the potential for superoxide-mediated degradation of NO and formation of peroxynitrites. In addition to its positive effects on NO. oestrogen has been shown to promote the release of other vasodilator agents from endothelium.

There are two known classical oestrogen receptors ERα and ERß both widely distributed throughout the body. Oestrogen, or other oestrogcnic ligands. bind to these nuclear receptors in the cytosol. which allows the receptor to enter the nucleus and bind to response elements on DNA, and modulate gene transcription. ERα and ERß bind to the same oestrogen response elements (therefore affecting transcription of the same genes. However, they are functionally distinct and will not necessarily affect these genes in the same direction or with the same potency. Although ERα and ERß are both expressed throughout the vasculature ERB is the receptor that predominates in this tissue, particularly in women. In addition, there are specific functional domains on the two receptor proteins that have a degree of divergence in their homology, which may affect binding of oestrogenic ligands. This is illustrated by the greater binding affinity of isoflavones for ERß compared with ERa .

Since ERa and ERß have different tissue distributions and binding affinities, it seems probable that the protective effects of oestrogen, or indeed oestrogen-like compounds, on the endothelium would vary with receptor type.

ERa appears to be the most important receptor for the protective effects of oestrogen in the endothelium.

Since isoflavones have a greater binding affinity for ERp compared with ERa then it might be expected that any protective effect of isoflavones against vascular injury would be weak compared with that of oestrogen, unless the isoflavone- ERß conformation induced a greater affinity for the oestrogen response element than the oestrogen- ERß conformation. Isoflavones bind more effectively to ERß compared with ERa, but they are also 1000 times more potent at generating transcriptional activity via ERß compared with ERa, due to selective recruitment of co-regulators to ERp. In addition, isoflavones are more effective at triggering transcriptional repression rather than activation, suggesting that isoflavones may repress transcription of some genes that are normally activated by ERa.

Hall WL et al 2005, Nutrition Research Reviews, 18, 130-144

Jasmonate —

Jasmonates are essential phytohormones for plant development and survival. They are the major lipid in the jasmine scent. However they are important in plant development processes, response to environmental stress, wounding , water deficit, and pathogen and pest attacks, root growth, fruit ripening, tendril coiling, reproductive development and senescence. .

They are synthesised from linolenic acid, and are structurally related to prostaglandins.

A paper in Nature

Chini et al 207 The Jaz family of repressors is the missing link in jasmonate signalling. Nature vol 448, 666-671 ,

This paper discusses the negative regulatory feed back loop that jasmonate is involved in the plant.

Plant Secondary Metabolites
Lignans —

Investigations into the health effects of whole flaxseed or flaxseed products (for example, defatted flaxseed meal, flaxseed extracts) in human clinical trials and animal models have shown beneficial changes in blood lipid profiles and protection against some types of cancer. However, such studies do not show which flaxseed component(s) the benefits can be attributed, as flaxseed contain at least three components that are of health interest: soluble fibres or mucilage (about 6 % of dry weightp); high amounts of a-linolenic acid, an n-3 PUPA (about 20 % of dry weight); and the plant lignan secoisolariciresinol diglucoside, about 1 % of dry weight). Flaxseed also contains small amounts of other lignans, namely pinoresinol, lariciresinol and matairesinol, and although secoisolariciresinol diglucoside is the predominant lignan, the others may also contribute to health effects.

Flaxseed is the richest source of secoisolariciresinol diglucoside; however, the amount of secoisolariciresinol diglucoside in flaxseed varies between different cultivars and in most studies that examined the health effects of flaxseed or its products, the concentration of lignans was not determined.

Studies have shown that in defatted flaxseed extracts secoisolariciresinol diglucoside exists in oligomeric form largely in ester linkages to 3-hydroxy-3-methylglutaric acid(IO) and ¬cinnamic acid and .with other phenolic secoisolariciresinol diglucoside oligomers

The ability to quantify secoisolariciresinol diglucoside content in flaxseed extract sources enables an association to be drawn between secoisolariciresinol diglucoside amounts and the putative health effects of flaxseed lignans.

After ingestion, the plant lignan secoisolariciresinol diglucoside is converted to mammalian lignans by bacteria in the human colon. Secoisolariciresinol diglucoside first undergoes hydrolysis to yield the aglycone plant lignan secoisolariciresinol which is then converted to enter¬odiol (ED) and enterolactone (EL), first by dehydroxylation and demethylation to yield ED, which can then be oxidised to form EL(13) ED and EL can undergo further phase I and phase II biotransformation with extensive formation of glucuronide and sulfate conjugates(l4.IS), though the role of these metabolites in inducing biological effects is presently unknown.

The structural similarity of EL and ED to the most predomi¬nant and active form of oestrogen in the body, oestradiol, allows these lignans to bind to oestrogen receptors and exert weak oestrogenic or anti-oestrogenic effects’?’, However, the micromolar concentrations required to modulate oestrogen receptor activity in vitro is much higher than the serum EL and ED levels (nanomolar range) normally measured in the general populatio.

Nonetheless, recent studies provide scientific evidence of dietary sources of lignans as modulators of oestrogen receptor signalling in vivo

EL and ED also possess antioxidant activity.

Adolphe et al 2010 Health effects with consumption of the flax lignan secoisolariciresinol diglucoside British J Nutrition vol 103, 929-938

Mianserin & Lifespan —

In a remarkable study , 88, 000 chemicals were tested to see if they could extend the life span of the worm ( caenorhabditis elegans). This worm may normally live for up to 3 weeks. Of all the drugs tested only the anti-depressant mianserin significantly extended the worms life span by almost a third.

Mianserin is a blocker of the neural signalling by the neurotransmitter serotonin.

Further studies on the mechanism show analogies with nutritional deprivation which in appropriate circumstances may also extend life span.

Petrascheck et al 2007 An antidepressant that extends lifespan in adult caenorhabditis elegans Nature vol 450, pp 553-7

Photosynthesis & Witt —

During the second half of the twentieth century, great strides were made in revealing the molecular details of oxygen-generating photosynthesis, the basis of almost all life on Earth. Horst Witt was one of the prime movers behind this revolution in understanding. His obituary appears in Nature 2007, vol 448, p425

Witt was born in 1922 in Bremen, Germany.

Witt chose oxygenic photosynthesis as his lifelong research topic. Inspired by the methods pioneered by George Porter and Ronald Norrish, he embarked on work with the technique of flash spectrophotometry. Using algae, in 1955 he discovered reactions of chlorophylls, carotenoids and cytochromes that occurred in microseconds. By 1961,he along with Lou Duysens and of Bessel Kok, demonstrated a scheme with two photochemical reaction centres in series

At photosystem II, electrons are removed from water, generating a strong oxidant, oxygen. At photosystem I, the electrons are used to produce a strong reductant, NADPH (and thence sugars). The energy difference between the strong oxidant and the strong reductant powers all oxygen-based life.

During the ensuing years,his team of investigators marked off milestones in photosynthesis research. They found that excess light energy is disposed of harmlessly as heat through protective carotenoids. They discovered that the reactive pigment of photosystem II is chlorophyll a: its cationic form extracts electrons from the active site of water oxidation, with kinetics that depends on the electrostatics of charge accumulation. And they identified plastoquinone as an electron acceptor in photosystem II, where it functions as a one-to-two electron gate and as a mobile carrier between the two photosystems.

A further success was to demonstrate reactions with associated proton uptake and release at opposite sides of the membrane, as shown earlier by Peter Mitchell, which generated the proton-motive force required for the synthesis of ATP.

Rut it was the mechanism of water oxidation that remained Witt’s career-long preoccupation. The manganese cluster In photosystem 11 is charged up with four oxidizing equivalents before it reacts with two water molecules, releasing dioxygen. Witt and his co-workers contributed valuable information on many aspects of the mechanism, including the valence changes of manganese, associated electrostatic changes and effects of extrinsic reductants. Despite these and other contributions from many laboratories around the world, understanding the detailed mechanism has remained a major challenge.

Witt’s early attempts to crystallize photosystem II were fruitless, and it seemed that the game would be lost to others However, crystals of photosystem I were eventually obtained, a trimeric structure with multiple subunits, diverse electron co-factors, about 100 chlorophyll molecules and many carotenoids. Later photosystem 11 was crystallised.

Insights into a system central to life.

Junge and Rutherford 2007, Nature p425

Photosynthesis —

Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems

Engel and colleagues

Nature vol 446, 12th April 2007

This summary is taken from Nature. Whilst the detailed chemistry is unlikely to appeal to most Nutritionists this is a fundamentally important process for life. It is therefore worth having a look at and even 10% uptake is valuable. Nutrition is a science and also we should be educated .

If nothing else knowing of the Fenna-Matthews-Olson (FMO) bacteriochlorophyll complex, will give you an edge in any Pub quiz.

Photo synthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated. The energy transfer mechanism is often described by semi classical models that invoke ‘hopping’ of excited-state populations along discrete energy levels’”. Two-dimensional Fourier transform electronic spectroscopy”’ has mapped” these energy levels and their coupling in the Fenna-

Matthews-Olson (FMO) bacteriochlorophyll complex, which is found in green sulphur bacteria and acts as an energy ‘wire’ connecting a large peripheral light-harvesting antenna, the chlorosome, to the reaction centre. The spectroscope data clearly document the dependence of the dominant energy transport pathways on the spatial properties of the excited-state wavefunctions of the whole bacteriochlorophyll complex. But the intricate dynamics of quantum coherence, which has no classical analogue, was largely neglected in the analyses — even though electronic energy transfer involving oscillatory populations of donors and acceptors was first discussed more than 70 years ago, and electronic quantum beats arising from quantum coherence in photo synthetic complexes have been predicted and indirectly observed. Here we extend previous two-dimensional electronic spectroscopy investigations of the FMO bacteriochlorophyll complex, and obtain direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes within this system. The quantum coherence manifests itself in characteristic, directly observable quantum beating signals among the excitons within the Chlorobium tepidum FMO complex at 77 K. This wavelike characteristic of the energy transfer within the photo synthetic complex can explain its extreme efficiency, in that it allows the complexes to sample vast areas of phase space to find the most efficient path..

The system is essentially involved in a process wherein many senses are sensed at the same time and allowing the most effective transfer of energy to the correct locus.

This mechanism contrasts with a semi classical ‘hopping’ mechanism through which the excitation movesstepwise from exciton state to exciton state, dissipating energy at each step, which would be similar to a classical search where only one state can be occupied at any one time. Such a mechanism also raises the possibility of non-local events.

The FMO light-harvesting complex provides an opportunity to apply more complete energy transfer theories that invoke non-markovian dynamics and include coherence transfer. Such theories need to include wavelike energy motion owing to long-lived coherence terms, alongside the population transfer included in current models. Further, the observed preservation of coherence in this photosynthetic system requires us to redefine our description of the role of electron-phonon interactions within photosynthetic proteins. In particular, the protein may not only enforce the structure that gives rise to the couplings, but also modulate those couplings with motions of charged residues and changing local dielectric environments, which will change exciton energies and promote coherence transfer.

Plant Hormones —

Recent advances and emerging trends in plant hormone signalling

Aaron Santner ‘ & Mark Estelle have reviewed plant homones in Nature 25th June 2009

In eating frit and vegetables there are many different molecules whose function when eaten by man is unknown included in these are plant hormones.

Plant growth and development is regulated by plant hormones. During the last 15 years the number of known plant hormones has grown from five to at least ten. Furthermore, many of the proteins involved in plant hormone signalling pathways have been identified, including receptors for many of the major hormones. Strikingly, the ubiquitin-proteasome pathway plays a central part in most hormone-signalling pathways. In addition, recent studies confirm that hormone signalling is integrated at several levels during plant growth and development.

Because plants have a sessile lifestyle, they must adjust to numerous external stimuli and coordinate their growth and development accordingly. The plant hormones, a group of structurally unrelated small molecules, are central to the ntegration of diverse environmental cues with a plant’s genetic program. The ‘classical’ phytohormones, identified during the first half of the twentieth century, are auxin, abscisic acid, cytokinin, gibberellin and ethylene.

More recently, several additional com¬pounds have been recognized as hormones, including brassinoster¬oids, jasrnonate, salicylic acid, nitric oxide and strigolactcnes

Plants also use several peptide hormones to regulate various growth responses, Most hormones are involved in many different processes ( hormone synthesis, transport and signalling pathways, as well as by the diversity of interactions among hormones) to control growth responses. throughout plant growth and development. Genetic screens have identified many of the pro¬teins involved in hormone signalling

Receptors for auxin, gibberellin , jasmonate and abscisic acid have now been identified. Some hormones (cytokinins, ethylene and the brassinosteroids) use well-characterized signalling mechanisms.

The auxin and jasmonate receptors, as well as proteins in gibberellin signalling, have highlighted a novel mechanism for hormone perception in which the ubiquitin–proteasome pathway.

Has this any relevance to human nutrition? Who knows , but we do know that eating fruit and vegetables is good for health, and these plant hormones may be of biological value.

Santner and Estelle 2009 Recent advances and emerging trends in plant hormone signalling. Nature vol 459 pp 1071-78

Theobromine —

Chocolate is a delicacy which is enjoyed by most people and also other animal species. Chocolate is not healthy for dogs who love this treat.

The reason is their slow metabolism of the methyl xanthnine alkaloid Theobromine. The amount of theobromine in a product depends on whether it is bakers chocolate

(390-450 mg / oz chocolate ) or dark chocolate or milk chocolate ( 44-60 mg / oz chocolate ) in decreasing order. Dogs take some 20 hours to eliminate a dose of theobromine.

The toxicity of theobromine is dose dependent. The toxic dose is of the order of 100-200 mg / kg though lower doses have been shown to be toxic. If a 40 lb weighing dog was to eat say an 8 oz ( 240 g ) bar of dark chocolate it would within a few hours develop severe abdominal symptoms. Eating more may lead to death. The theobromine is a cardiovascular and central nervous system stimulant. While theobromine and caffeine are similar in that they are related alkaloids, theobromine is weaker in both its inhibition of cyclic nucleotide phosphodiesterases and of adenosine receptors.

The advise and care of a Vet is essential in these cases. Intravenous fluids, activated charcoal to diminish absorption and anti seizure drugs may be required.

Toxicity —

An important subsidiary issue in nutrition is toxic substances which may be ingested, possibly along with food. This is a vast field but a recent and very well reviewed book is

How everyday products make people sick: Toxins at home and in the workplace

By Paul D Blanc.

University of California Press 2007

reviewed in Nature by Robbins ( Nature 446, 22nd March 2007 p377 )

The emphasis is on the limited manner that the body can respond to poisons and pathogens. There are such variables as length of exposure, amount of toxin exposed to, the mode of ingestion and the metabolism of the toxin. Examples of toxins are mercury poisoning, asbestosis, bleaching compounds, glue solvents, carbon disulphide and organic manganese compounds.

Whole Grain Phytochemicals —

A whole grain consists of the intact, ground, cracked, or flaked caryopsis, whose principal anatomical components, the starchy endosperm, germ. and bran-are present in the same relative proportions as they exist in the intact caryopsis. Whole grain food products can be intact, consisting of the original composition. of bran. germ, and endosperm. throughout the entire lifetime of the product, or reconstituted, in. which one or more of the original components of a whole grain is recombined 10 the relative proportion naturally occurring in the grain kernel. Increased consumption. of whole grains has been associated with reduced risk of major chronic diseases including cardiovascular disease, type 11 diabetes, and some cancers. Whole grain foods offer a wide range of phytochemicals with health benefits that are only recently becoming recognized. The unique phytochemicals in whole grains are proposed to be responsible for the health benefits of whole grain consumption. In this paper; whole grain phytochemicals and the health benefits associated witli their consumption are reviewed.

The whole grain phytochemicals which the autor identify as being of value include

Phenolics , phenolic acids, alkenylresorcinols , flavonoids, Carotenoids, vitamin E, ?-oryzanol and dietary fibre.

Okarter and Liu (2010 ) Health Benefits Phytochemicals of Whole Grain. Critical Reviews in Food Science and Nutrition vol 50, 193-208

Zeaxanthiin, Lutein —

Thurnham has written a very interesting review of macular zeaxanthins and luteins.

Thurnham (2007) Macular zeaxanthins and luteins-a review of dietary sources and bioavailability and some relationship with macular pigment optical density and age-related macular disease. Nutrtional Research Reviews vol 20 163-179.

The retina is unique in the human body in containing three xanthophyll carotenoids: 3K,3’R-zeaxanthin. meso-zeaxanthin (MZ) and lutein.

We eat 1 to 3 mg lutein per day and the lutein: zeaxanthin ratio in the diet is about 5:1. Xanthophyll pigments occur widely in vegetables and fruits but MZ is found in only a few foods such as the shrimp carapace and fish skin.

In spite of the amounts of the different xanthophylls in the diet, zeaxanthin and MZ occur in approximately equal amounts in the eye, and their combined concentration can exceed that of lutein. A number of studies have used single and mixed sources of the pure xanthophylls to achieve steady-state plasma responses. Mostly these have been with lutein and zeaxanthin but two using MZ are also described.

Vegetables are the richest source of dietary lutein Intervention studies with eggs, which are a good source of zeaxanthin. suggest that the xanthophyll carotenoids in egg yolk may be more bioavailable than those in other foods

Very limited information from human studies of MZ-containing supplement. suggests that MZ is less well absorbed than zeaxanthin. Thus plasma responses may not reflect true absorption if it takes MZ longer to equilibrate with body tissues than the other xanthophylls and competition with zeaxanthin may lower the relative concentrations of MZ in plasma.

It would be nice if a xanthophyll carotenoids rich diet kept the retrina healthy, but this has yet to be proven


Back to top