Flavins nomenclature

Flavin nomenclature (see Scheme 1) abounds in atrocities, which have become so commonly used that it seems an idle task to discuss them, but nevertheless this problem must be tackled. 

PHYSICAL ORGANIC CHEMISTRY NOMENCLATURE FLAVANONE 3/3-HYDROXYLASE FLAVINS AND DERIVATIVES Flavokinase,... 

Lawton, M. P., J. R. Cashman, T. Cresteil, C. T. Dolphin, A. A. Elfarra, R. N. Hines, E. Hodgson, T. Kimura, J. Ozols, I. R. Phillips, R. M. Philpot, L. L. Poulsen, A. E. Rettie, E. A. Shephard, D. E. Williams and D. M. Ziegler. A nomenclature for the mammalian flavin-containing monooxygenase gene family based on amino acid sequence identities. Arch. Biochem. Biophys. 308 254-257, 1994. 

The spectra of oxidized glutathione reductase and of the 2-electron-reduced enzyme are shown in Fig. 1. This red intermediate, which has been shown to be functional in catalysis 39), will be referred to as EH2 designating a half-reduced active center it has also been referred to as F (S3, 53), but this can be confused with oxidized flavin in other nomenclatures. Its spectral characteristics are virtually identical with those of the analogous species of lipoamide dehydrogenase 34, 37, 64)- It has... 

Flavoenzymes constitute about 2% of all biological catalysts and are classified in several ways. One classification is based on EC number (enzyme nomenclature) and refers to the type of reaction catalyzed. More sophisticated classifications concern the inclusion of sequence, fold, and function. Historically, a distinction is made between simple and complex flavoenzymes (4). The latter proteins contain besides flavin other cofactors like heme, tetrahydrobiopterin, and metal ions. 

Lawton MP, Cashman JR, Cresteil T, Dolphin CT, Elfarra AA, Hines RN, Hodgson E, Kimura T, Ozols J, Phillips IR. A nomenclature for the mammalian flavin-containing monooxygenase gene family based on amino acid sequence identities. Arch Bioch Biophys 1994 308 254-257. 

Yellow (hence the name) prosthetic groups,//av/w adenine dinucleotide (FAD) and the somewhat less common flavin mononucleotide (FMN) are linked to protein in flavoproteins (Fig. 29), The nomenclature is not quite accurate since 6,7-dimethyl-isoalloxazine, which is responsible for the color, is not linked to ribose, as in the nucleotides, but to the corresponding sugar alcohol ribitol. In both FAD and FMN the 6,7-dimethyl-... 

The active component of the old yellow enzyme is riboflavin 5 -phosphate, usually called flavin mononucleotide and abbreviated FMN. This nomenclature is somewhat incorrect again, since we do not have a nucleotide, i.e. an N-glycoside of a ribose phosphate. In spite of this, the name and abbreviation have been adopted, and actually the close similarity to real nucleotides must be conceded. 

Scheme 1. Flavin and Flavocoenzyme nomenclature and modes of breakdown by mild and strong protolysis, photolysis and hydrogenolysis (R = H Loosely bound R = Protein [His, Cys] Covalently bound flavin)...

Derivatives of other l,n-dihydroflavins will be discussed in the chapter on flavin oxygen adducts (see below), where position n means a carbon atom substituted by a strongly electronegative group such as OH, OR, OOH, etc. The dilemma encountered in the determination of the redox state (chromophore = dihydroflavin, redox balance = flavoquinone) of such compounds, e.g. hydroxydihydrofiavins , has been discussed in the Nomenclature chapter (cf. above). 

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