Flavin-catalyzed reactions connected to folate metabolism: dimethlyglycine dehydrogenase (EC 1.5.99.1, DMGDH), sarcosine dehydrogenase (EC 1.5.99.2, SARDH), N-5,10-methylene-tetrahydrofolate reductase (EC 1.5.1.20, MTHFR) and methionine synthase reductase (EC 1.16.1.8, MSR). Structures depicted are from the human methionine synthase reductase (2qtl) as well as the N-5,10-methylene-tetrahydrofolate reductase from Thermus thermophilus HB8 (3apt).