There is growing recognition that many phenolic secondary metabolites present in foodstuffs may possibly exert beneficial effects on human health. This may to some degree be mediated via antioxidant actions, but a range of more specific pharmacological effects have also been proposed. Given this background, there may be favourable consequences for the general health of Western populations as a result of optimising the phenolic content of the diet. This paper reviews what is known of the function of phenolics both in the plant and in man. It also describes current understanding of the biosynthesis of phenolics in plants, with emphasis on where potential controlling steps may exist. Finally, advances in identification and isolation of the genes coding for phenolic biosynthetic enzymes or regulatory proteins are also summarised. Taken together, this information provides a basis for attempts to modify and optimise the phenolic content of food crops, using either conventional plant breeding along with manipulation of agronomic practices, or else the more targeted approaches of modern molecular biology.



© 2000 Society of Chemical Industry

Phenols in the plant and in man. The potential for possible nutritional enhancement of the diet by modifying the phenols content or profile

Publisher Summary This chapter discusses the results of the studies that permit some generalizations on the catalytic mechanism of glycoside hydrolases from widely differing sources and with different sugar and aglycon specificities and that have become available over the past 15 years. The strong inhibition of glycosidases by aldonolactones was first mentioned in 1940 by Japanese workers who studied β- D -glucosidases from Aspergillus (Taka-diastase) and almonds. Even though both of these groups of compounds are derived from normal substrates by only a minor modification of the glycon moiety, they are discussed together with pseudosubstrates because their reactions with glycosidases show, in many cases, unusual kinetic features. The information relevant to the mechanism of an enzyme-catalyzed reaction can, in general, only be obtained from irreversible inhibitors that react specifically at the active site, and thereby inactivate the enzyme. In many cases, inhibition studies were not carried out to obtain information on the reaction mechanism, but for other purposes. Thus, only inhibitors were tested that were considered suitable for the particular project, for example, studies on the biological function of the enzyme where glycosylamines and aldonolactones are unsuitable.

Glycoside Hydrolases: Mechanistic Information from Studies with Reversible and Irreversible Inhibitors

Phytoalexins: enzymology and molecular biology.

Potential Value of Plants as Sources of New Antifertility Agents II

Allelopathy in Agroecosystems

β-Glucosidases specific for isoflavone 7-O-glucosides have been isolated from garbanzo plants, Cicer arietinum L.



These aryl-β-glucohydrolases occur in the different organs of the plant as multiple molecular forms. The major isoenzymes of the roots, the leaves and the hypocotyl were purified to electrophoretic homogeneity. When subjected to isoelectric focussing in polyacrylamide gels the electrophoretically homogeneous glucohydrolases were found to consist of one or two major and several minor enzymically active molecular species.



In roots the β-glucohydrolase isoenzymes constitute a considerable portion of the extractable protein, so that purification to an electrophoretically homogeneous form is easily attainable.



All β-glucosidases analyzed possess molecular weights in the range of 125000 (ultracentrifugation) to 135000 (Sephadex G-200) and contain two subunits of molecular weight near 68000. The pH optimum for enzymic activity is 7–7.5 with a second optimum of 4.5–5. The isoelectric points of the various species range between pH 5.9 and 7.1. Staining for glycoprotein was positive.



Kinetic analysis demonstrated a pronounced specificity of the enzymes for aromatic substrates with glucose as the sugar moiety. α-Glucosides as well as disaccharides were not hydrolyzed at all. Isoflavone 7-O-glucosides are the most favoured substrates with a Km of 2 × 10−5 M, while the Km with aromatic glucosides (i.e. salicin, 4-nitrophenyl glucoside) are 100 times larger. In addition the β-glucosidases show a pronounced specificity for glucose in the 7-position of the flavonoid nucleus. Using isoflavone aglycones as substrates glucose transferase activity was also demonstrable.



The β-glucohydrolase activity is strongly inhibited by Hg2+. This inhibition is partially reversible and preferentially influences the Km values of the enzymes compared to to V. Ag+ glucono-1,5-lactone, ethyleneglycol monomethyl ether and glycerol are only weakly inhibitory, while glucose, p-chloromercuribenzoate and Cu2+ are without effect.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1975.tb02336.x

β‐Glucosidases from Cicer arietinum L.

This chapter will deal with various aspects of flavonoid turnover and degradation in higher plants and microorganisms. The microbial dissimilation of flavonoids has been a well understood area of biochemical research for many decades. It has been part of the more general field of microbial transformations of natural aromatic compounds, where it has been shown that all organic molecules are degraded by some form of life to maintain the carbon cycle of nature. Soil and sewage microflora are specifically adapted to perform this task. The results of microbial metabolism will be discussed here to outline the chemical principles governing flavonoid dissimilation and to relate them to the fate of flavonoids in higher plants.

Wolfgang Hösel

Papers

β‐Glucosidases from Cicer arietinum L.

Metabolism of Flavonoids

Characterization of cyanogenic glucosides and β-glucosidases in Triglochin maritima seedlings

Flavonoide aus Cicer arietinum L.

Über den umsatz von flavonolen und isoflavonen in Cicer arietinum