Flavin enzymology

Nowadays, a characteristically modified flavin, 5-deazaflavin (33,142), has gained much interest in flavin enzymology because it can replace natural flavin at many enzyme sites. This derivative, however, is no quinoid system and its radical has no thermodynamic stability. It is, therefore, a mutilated flavin retaining the 2e"-transfer (i.e. nicotinamidelike) properties only (cf. Table 2). The thia-analog, however, is an O2-stable dihydro derivative, which exhibits a stable radical, but no reversibly reducible oxidized form. Hence, it is also a mutilated flavin, but one which retains the e"-transferase activity only. 

As is borne out by these data, uncertainty about the site of substrate or inhibitor addition to the flavin in photochemistry and in enzymology is very similar. Moreover the adduct chromophores are absolutely identical in the photochemical and in the enzymic cases (159, 119). We may be far away from explaining these phenomena as functions of the molecular structures and physical properties of flavin, substrate and environment, but the model relevance of flavin photochemistry to a molecular understanding of flavin enzymology cannot be denied. 

Tu, S.-C. (1991). Oxygenated flavin intermediates of bacterial luciferase and flavoprotein aromatic hydroxylases enzymology and chemical models. Adv. Oxygenated Processes 3 115-140. 

Selected entries from Methods in Enzymology [vol, page(s)] Determination of FMN and FAD by fluorescence titration with apoflavodoxin, 66, 217 purification of flavin-adenine dinucleotide and coenzyme A on p-acetoxymercurianiline-agarose, 66, 221 a convenient biosynthetic method for the preparation of radioactive flavin nucleotides using Clostridium kluyveri, 66, 227 isolation, chemical synthesis, and properties of roseoflavin, 66, 235 isolation, synthesis, and properties of 8-hydroxyflavins, 66, 241 structure, properties and determination of covalently bound flavins, 66, 253 a two-step chemical synthesis of lumiflavin, 66, 265 syntheses of 5-deazaflavins, 66, 267 preparation, characterization, and coenzymic properties of 5-carba-5-deaza and 1-... 

Since the initial observation of flavin radical species by Michaelis and coworkers the involvement of flavins in one-electron oxidation-reduction processes in biological systems has occupied the attention of workers in the field of redox enzymology up to the present time. Flavin coenzymes occupy a unique role in biological oxidations in that they are capable of functioning in either one-electron or two-electron transfer reactions. Due to this amphibolic reactivity, they have been termed in a recent review to be at the crossroads of biological redox processes. 

Flavoenzymes may be ideal model systems for the development of new tools to be made available for the study of enzymes in general. One example may be the use of cholesterol oxidase for single molecule enzymology, which exploits the flavin fluorescence changes during the catalytic cycle (29). 

The term flavin stands for the yellow redox-active subgroup of the first coenzyme ever to be elucidated in terms of molecular structure. The heroic period of redox-enzymology of the early thirties ended in Hugo Theorell s 172—175) description of the first enzyme ever to be split reversibly to yield coenzyme and apoprotein. This was the NADPH-... 

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