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Effect of Riboflavin Status on Hepatic Activities of Flavin-Metabolizing Enzymes in Rats^1,2,

Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322

The effect of riboflavin status on hepatic activities of the relatively substrate-specific flavokinase and FAD synthetase and the relatively nonspecific FMN phosphatase and FAD pyrophosphatase was investigated in weanling, male Sprague-Dawley rats fed 0, 5, 15, 30 and 60 µg riboflavin/15 g diet for 1, 3 and 5 weeks. Flavokinase activity was determined by using [¹⁴C]riboflavin and ATP as substrates and measuring product [¹⁴C]FMN after incubation and separation by high performance liquid chromatography. Similarly, FAD synthetase activity was determined by using [³H]ATP and FMN and quantitating [³H]FAD formed. Flavokinase activities among all groups were similar after only 1 week of feeding experimental diets; by 3 weeks, activities were depressed to about 60% of normal in animals that received suboptimal riboflavin; by 5 weeks, activity of rats fed riboflavin-free diet was further decreased to about 40% of normal. FAD synthetase activities were unaffected by riboflavin status at 1 and 3 weeks; however, at 5 weeks, activities were moderately decreased to 85, 65 and 52% of normal with rats which had received 15, 5 and 0 µg riboflavin/15 g diet, respectively. FMN phosphatase and FAD pyrophosphatase activities decreased with age, but were not influenced by riboflavin status at any period. Overall results indicate the effect of increasing severity of riboflavin deficiency is greater with flavokinase, which is physiologically rate-limiting in the biosynthesis of flavocoenzymes, than with FAD synthetase.

KEY WORDS: • riboflavin status • flavokinase • FAD synthetase • FMN phosphatase • FAD pyrophosphatase

¹ Supported in part by a grant from the National Institutes of Health (AM26746) and in part by the Coca-Cola Company.

² Presented in part at the 74th annual meeting of the American Society of Biological Chemists, San Francisco, CA. June. 1983.

³ To whom reprint requests should be sent.

Manuscript received 9 May 1983.