Progress in the chemistry and molecular biology of flavins and flavocoenzymes.

Abstract

AbstractAn attempt is made to create a basis for the understanding of flavin‐ (Vitamin B2‐) dependent oxidations in terms of molecular structure. The main points of this survey can be summarized as follows: (a) The flavins must be differentiated according to their redox states (quinone state, radical state, hydroquinone state), since configuration, energy content of the tautomeric forms, metal affinity etc., alter drastically during reduction. – (b) The methyl group on C‐8 of the flavoquinone is reactive. – (c) The electron transfer properties of the flavin system frequently depend on the coupling of secondary redox systems to the apoprotein. This interaction thermodynamically stabilizes the half‐reduced state of the flavin. – (d) Numerous novel flavin types, among them stabilized free radicals, have become available through syntheses at the dihydro stage. – (e) Reaction of the flavin radical with O2 is slow as long as no disproportionation occurs, i.e. the fast flavin autoxidation proceeds via the dihydro state. – (f) The flavin nucleus gains affinity for heavy metal ions only by the acceptance of one, and only one, electron. – (g) Redox activity and contact with the flavin coenzyme have been confirmed for Fe and Mo, which occur in flavoproteins. The properties of the metal coordination sphere are determined primarily by sulfur‐containing groups of the apoprotein.