Methylation of deoxyuridylate to thymidylate involve one carbon metabolism. Cofactor in one carbon metabolism is:

FH4 is an intermediate in reactions involving the transfer of one-carbon units from a donor to an acceptor. One-carbon units enter the folate pool principally the serine hydroxymethyltransferase reaction which requires pyridoxal phosphate as cofactor. The most impoant clinically is the methylation of deoxyuridylate to thymidylate, catalyzed by the enzyme thymidylate synthase. This reaction is an essential step in the synthesis of DNA. Metabolic Systems Requiring Folic Acid Coenzymes: Serine ? glycine Thymidylate synthesis Histidine catabolism Methionine synthesis Purine synthesis Ref: Green R. (2010). Chapter 41. Folate, Cobalamin, and Megaloblastic Anemias. In J.T. Prchal, K. Kaushansky, M.A. Lichtman, T.J. Kipps, U. Seligsohn (Eds), Williams Hematology, 8e.