Flavin coenzymes general functions

The flavin-containing coenzymes are similar in importance to the pyridine coenzymes as functioning in hydrogen transport. In general the flavin coenzymes mediate hydrogen transport between coenyzmes, rather than between substrates, although their function in anaerobic bacteria and certain other tissues indicates that they may also play an important role in hydrogen transport at the substrate level. 

In 1978, Caltech s W. A. Goddard proposed a different mechanism for the hydroxylation of phenolic compounds and attempted to show how flavin coenzymes carry out such oxidations. It is a theoretical proposal based on wave functions and quantum mechanics using generalized valence bond theory, applied to biological problems (297). An example is shown in Fig. 7.7 for the oxidation of phenol to catechol. 

The aromatic hydroxylases or mixed-function oxidases are no exception to the above generalization. For maximum activity they require a transition metal ion and an electron donor such as one of the pyridine or flavin nucleotide coenzymes further, they probably utilize molecular oxygen as the source of the hydroxylic oxygen an example is the liver microsomal hydroxylating system (27). As yet there is no comprehensive explanation to cover the mode of action of these enzymes, for on the one hand there are the specific hydroxylases which catalyze such conversions as L-phenylalanine to L-tyrosine (26) or tryptophan to 5-hydroxytrypto-... 

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