Flavin adenine dinucleotide oxidation states

The flavin coenzyme occurs in each of the oxidases discussed here as flavin adenine dinucleotide (FAD). The R group attached to is adenosyldiphosphoribityl. The flavin nucleus can exist in three redox states, each of which can adopt three ionization states (8, 9). Only two redox states—fully oxidized and fully reduced see Equation 1)—are kinetically important in the simple flavoprotein oxidases under discussion. 

Flavins (El) catalyze many different bioreactions of physiological importance [7-9]. Riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD) have the 7,8-dimethyl isoalloxazine ring in common but differ in the side chain attached to NIO. With their five redox states, fully oxidized, one-electron reduced semiquinoid (F1H and F1 ), and fully reduced hydroquinone (FIH2 and F1H ), flavins are involved in one-electron and two-electron transfer reactions [10]. 

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