The Effects of Galactoflavin on Riboflavin Enzymes and Coenzymes.

This is a record of the effects of feeding galactoflavin on the concentrations of riboflavin-containing coenzymes and enzymes in liver and kidney. Galactoflavin was shown by Emerson, Wurte, and Johnson (1) to produce a riboflavin deficiency in rats which is reversible by excess dietary riboflavin. Slight inhibitory effects of galactoflavin were later found by Kearney (2) on the enzymatic activities of several flavoproteins purified from yeast, kidney, or snake venom. The enzyme inhibitions in vitro were not sufficiently large to account for the over-all effects of galactoflavin fed to rats. In order to find out whether greater inhibitions occur in viva, rats were given galactoflavin until signs of riboflavin deficiency appeared; the tissues were then analyzed for flavin mononucleotide, flavin adenine dinucleotide, Dand L-amino acid oxidases, glycolic acid oxidase, reduced triphosphopyridine nucleotide dehydrogenase,l and reduced diphosphopyridine nucleotide dehydrogenases. In addition tissue extracts were examined chromatographically to see whether galactoflavin had replaced riboflavin in either the free or the combined (coenzyme) form. The feeding experiments were supplemented by studies in vitro with the galactoflavin anologue of FMN,2 galactoflavin monophosphate. It was found that this coenzyme analogue is capable of partially reactivating the apoenzymes of liver and yeast TPNH dehydrogenases. Riboflavin nutrition has certain special features that are essential for understanding the effects in vivo of galactoflavin. For each tissue there is (a) a limiting upper level for flavin content which is not exceeded, no matter how much riboflavin is fed, and (b) a limiting lower level below which flavin content will not fall on a riboflavin-free diet, no matter how long continued (3). The characteristic upper and lower limiting levels may differ by as little as 35% in some tissues, such as brain, whereas, in liver, at the other extreme, there is a $-fold difference between “ceiling” and “floor” (4). As a rule a greater proportion of FMN than of FAD is lost in deficiency; free riboflavin is present at very low levels (4). When an animal is placed on a riboflavin-free diet it