Effect of vitamin B2 deficiency on rat liver dihydropyrimidine dehydrogenase activity.

Effect of vitamin B2 deficiency on rat liver dihydropyrimidine dehydrogenase was investigated. It was found that the purified enzyme contains 2 mol flavin per molecule, which consists of equal proportions of flavin-adenine dinucleotide (FAD) and riboflavin 5'-phosphate (FMN). When rats were fed on a vitamin B2-deficient diet for 5 weeks, dihydropyrimidine dehydrogenase activity in the liver was diminished, followed by a decrease in enzyme concentration. Moreover, the addition of exogenous FAD or FMN did not restore the activity. Thus endogenous flavin may regulate the enzyme half-life or synthesis. Lowering of dihydropyrimidine dehydrogenase activity in the livers of rats fed on a vitamin B2-deficient diet did not affect the uridine, uracil and sigma UMP (the sum of acid soluble uracil 5'-nucleotides) pool in liver.