Regulation of riboflavin-metabolizing enzymes in riboflavin deficiency.

FASS, STEVEN, AND RICHARD S. RIVLIN. Regulation of riboflavinmetabolizing enzymes in ribuj?auin de_ficiency. Am, J. Physiol. 217(4) : 988-99 1. 1969.-The effects of riboflavin deficiency in rats on the hepatic activities of flavokinase, FAD pyrophosphorylase, and FMN phosphatase, three enzymes involved in riboflavin metabolism, have been measured and compared to the hepatic concentrations of FAD, FMN, riboflavin, and protein. Of the enzymes involved in FMN and FAD biosynthesis, the activity of the first, flavokinase, is depressed in deficient animals to 6070 of normal, whereas the activity of the second, FAD pyrophosphorylase, is elevated to 15070 of normal. The FMN-degrading enzyme, FMN phosphatase, is unaffected by riboflavin deficiency. Refeeding of riboflavin to deficient animals restores the activities of both Aavokinase and FAD pyrophosphorylase to normal. The data demonstrate that riboflavin deficiency has selective effects upon the activities of liver enzymes involved in riboflavin metabolism. It is suggested that these effects may conshtute a possible adaptive mechanism for conserving FAD in riboflavin deficiency.