Riboflavin is linked to the metabolism of B-vitamins involved in homocysteine remethylation and transsulfuration. Riboflavin is transformed to FMN and FAD by the action of riboflavin kinase (EC 2.7.1.26) and FAD synthase (EC 2.7.7.2.). FMN and FAD are cofactors for vitamin B6, cobalamin and folate metabolizing enzymes. Vitamin B6 and cobalamin serve as cofactors for enzymes involved in homocysteine metabolism, while folate serves as a one-carbon donor for the remethylation of homocysteine. Abbreviations: Cbl(I), cob(I)alamin; Cbl(II), cob(II)alamin; CBS, cystathionine β-synthase; CH2-THF, 5,10-methylenetetrahydrofolate; CH3-THF, 5-methyltetrahydrofolate; CL, cystathionine lyase; Cys, cysteine; FS, FAD synthase; Met, methionine; MS, methionine synthase; MSR, methionine synthase reductase; MTHFR, 5,10-methylenetetrahydrofolate reductase; PLP, pyridoxal-5'-phosphate; PMP, pyridoxamine-5'-phosphate; PNP, pyridoxine-5'-phosphate; PPO, pyridoxine-5'-phosphate oxidase; RK, riboflavin kinase; THF, tetrahydrofolate.