1.5-Dihydroflavin adenine dinucleotide

Figure 4.2. The flavin coenzymes, flavine adenine dinucleotide/dihydroflavine adenine dinucleotide (FAD/FADH2), and flavin mononucleotide/dihydroflavin mononucleotide (FMN/FMN). The locations of N(5), N(10), and C(4a) are indicated. The groups Q are important only for binding and orientation in...

In order to be recycled, GSSG has to be reduced by glutathione reductase. The mechanism of the reaction has been resolved mainly by X-ray diffraction studies [15]. From the juxtaposition of the reactive moiety, it appears that the electrons from dihydroflavin adenine dinucleotide (FADH) will reduce an intramolecular disulfide bond in the enzyme forming 2 SH-groups which in turn will reduce the GSSG disulfide. 

Unusual features of riboflavin as recorded by some researchers include (1) High levels in liver inhibit tumor formation by azo compounds in animals (2) free radicals are formed by light or dehydrogenation flavine semiquinone dihydroflavin+ (3) free vitamin is found only in retina, urine, milk, and semen (4) substitution of adenine by other purines and pyrimidines destroys activity of flavin adenine dinucleotide (FAD) ... 

Flavin adenine dinucleotide (FAD) and its reduced form dihydroflavin (FADH2) participate in a large number of oxidation/reduction reactions in metabolism150. The structure of the reduced form has a distinct enamine feature that has been hypothesized to participate in covalent bonds with a number of substrates. 

---