Fungi, enzymatic reactions

Besides the most widely used catalytic reductions of dienes and polyenes there are some other ways to saturate the C=C double bonds in these molecules. One of these rarely used methods is the enzymatic or microbial reduction. In the presence of bacteria and fungi the reactions progress just as over any classical catalysts. 

Biological degradation—fungi, bacteria, insects, termites Enzymatic reactions—oxidation, hydrolysis, reduction Chemical reactions—oxidation, hydrolysis, reduction Mechanical—chewing... 

The aim of biosynthetic experiments with fungal metabolites is to establish the structure of the building blocks, the order in which they are assembled, the way in which chains are folded to form the carbon skeleton and the sequence interrelating precursors with the final metabolite. Biosynthesis is concerned with both sequences and reaction mechanisms. The sequence of the biosynthetic events, the role of intermediates and the stereochemistry of enzymatic reactions can be studied with appropriately isotopically-labelled substrates and with structural analogues of the natural intermediates. The chemical enzymology of individual steps and the role of key components and structures of the enzyme may be studied with isolated enzyme systems obtained from fungi. The features that determine the function of the enzyme and which control its activity may be determined by genetic studies in which mutants play an important role. 

Cells are able to cany out all of the functions of life. During cell duplication (reproduction), the DNA is replicated (one double-stranded molecule is converted to two double-stranded molecules) by specific enzymatic reactions, and the newly formed DNA is separated into two separate cells produced by growth and division of the former single cell. In bacteria, this asexual process of reproduction is the primary means of multiplication to produce new individuals. In contrast, protists, plants, fungi, and... 

FIGURE 18-6 Chemical structures of major sterols and cholesterol derivatives. The major sterols in animals (cholesterol), fungi (ergosterol), and plants (stigmasterol) differ slightly in structure, but all serve as key components of cellular membranes. Cholesterol is stored as cholesteryl esters in which a fatty acyl chain (R = hydrocarbon portion of fatty acid) is esterified to the hydroxyl group. Excess cholesterol is converted by liver cells into bile acids (e.g., deoxycholic acid), which are secreted into the bile. Specialized endocrine cells synthesize steroid hormones (e.g., testosterone) from cholesterol, and photochemical and enzymatic reactions in the skin and kidneys produce vitamin D. 

Plant secondary metabolites may inhibit specific enzymes, either in plants or in other species such as fungi or animals. In some cases, this appears to be the sole mode of action of the metabolite, whereas in others, enzyme inhibition forms part of a suite of effects. It must be noted, however, that the specificity and in vivo biological relevance of some findings remains questionable. An example of this is the inhibition of a variety of enzymatic reactions, including plant hormone biosynthetic enzymes, catalase, maltase and phosphatase by phenolics and phenolic acids (Macias et al, 2007). 

Polyporic acid is biosynthesised by condensation of two molecules of phenylpyruvic acid in the shikimate pathway via the intermediate 2,5-diphenyl-3-hydroxy-4-oxohex-2-enoic acid and by oxidation of the resulting hydroquinone. Terphenylquinones are transformed by enzymatic reactions into pulvinic acids and many other products, some of which are also characteristic pigments of lichens and fungi. 

DKPs are simple and easy to obtain and are quite common by-products of synthetic, spontaneous, and biological formation pathways. DKP formation has been well documented as side reactions of solid-phase and solution-phase peptide synthesis. In addition, DKPs have been shown to be decomposition products of various peptides, proteins, and other commercial pharmaceuticals. Cyclic dipeptides were found to be present in solutions of human growth hormone, bradykinin, histerlin, and solutions of agents within the classes of penicillins and cephalosporins. " DKPs are also enzymatically synthesized in several protists and in members of the plant kingdom. Hydrolysates of proteins and polypeptides often contain these compounds and they are commonly isolated from yeasts, lichens, and fungi. ... 

Monooxygenases are found in many living organisms bacteria, yeasts, insects, plants and mammal tissues. They are used for organic asymmetric reactions either in a more or less purified enzymatic form (cytochromes P-450) or in whole-cell microorganisms (bacteria, fungi). 

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