Relationship between changes in properties and contents of riboflavin derivatives of NADPH-cytochrome P-450 reductase in the liver microsomes of riboflavin-deficient rats.

Weanling male rats were fed a riboflavin-deficient diet for 5-8 weeks, and the decrease in NADPH-cytochrome P-450 reductase (FpT) activity in the liver microsomes was compared with the contents of riboflavin derivatives. The decrease of FpT activity for the reduction of cytochrome c was greater than that for the reduction of ferricyanide. The FpT's of riboflavin-deficient and control rats were indistinguishable in the Ouchterlony immunodiffusion test against anti-FpT, and were shown to have the same molecular weight of 78,000 by SDS-polyacrylamide slab gel electrophoresis. However, the purified FpT of the riboflavin-deficient rats contained 14.2, 4.9, and 1.9 nmol of FAD, FMN, and riboflavin per mg of protein, respectively, while that of the control rats contained 10.6 and 9.5 nmol of FAD and FMN per mg of protein, respectively. After riboflavin injection into the riboflavin-deficient rats, NADPH-cytochrome c reductase activity and FMN content of the FpT were restored to the control levels in 36 h, NADPH-ferricyanide reductase activity recovered in 18 h, and riboflavin content diminished in 18 h. On incubation of the purified FpT of the riboflavin-deficient rats with FMN, NADPH-cytochrome c reductase activity and FMN content were restored to those of control rats. These results indicated that a part of FMN in the FpT of the riboflavin-deficient rats was replaced with FAD and riboflavin.