Biochemical and molecular studies of human methenyltetrahydrofolate synthetase

5-FormylH4folate is administered clinically under the name Leucovorin in association with the antineoplastic agent 5-fluorouracil (5-FU) to enhance the cytotoxic effects of 5-FU. The combination has been shown to be superior to 5-FU alone in the treatment of patients with metastatic colorectal carcinoma. Methenyltetrahydrofolate synthetase (MTHFS) catalyzes the transformation of 5-formyl-tetrahydrofolate to methenylH4folate, which is the obligatory initial metabolic step prior to the intracellular conversion of 5-formylH4folate to other reduced folates and the increase in intracellular folate pools required for 5-FU potentiation. In the following paper, we will summarize results of biochemical and molecular studies of human MTHFS.