Riboflavin, FMN, and FAD are involved in the metabolism of niacin, vitamin B6, and folate. The synthesis of the niacin-containing coenzymes, NAD and NADP, from tryptophan involves the FAD-dependent enzyme, kynurenine 3-monooxygenase. Dietary deficiency of riboflavin can decrease the production of NAD and NADP, thereby promoting niacin deficiency. Conversion of vitamin B6 to its coenzyme, pyridoxal 5'-phosphate synthase, involves the enzyme, pyridoxine 5'-phosphate oxidase, which requires FMN. An enzyme involved in folate metabolism, 5,10-methylenetetrahydrofolatereductase, requires FAD to form the amino acid, methionine, from homocysteine.