5,10-Methenyltetrahydrofolate (5,10-CH-THF)

5,10-CH=THF is a form of tetrahydrofolate that is an intermediate in metabolism. 5,10-CH=THF is a coenzyme that accepts and donates methenyl (CH=) groups. It is produced from 5,10-methylenetetrahydrofolate by either a NAD+ dependent methylenetetrahydrofolate dehydrogenase, or a NADP+ dependent dehydrogense. It can also be produced as an intermediate in histidine catabolism, by formiminotransferase cyclodeaminase, from 5-formiminotetrahydrofolate. The combined activities of rabbit liver cytosolic serine hydroxymethyltransferase and C1-tetrahydrofolate synthase convert tetrahydrofolate and formate to 5-formyltetrahydrofolate. In this reaction C1-tetrahydrofolate synthase converts tetrahydrofolate and formate to 5,10-methenyltetrahydrofolate, which is hydrolyzed to 5-formyltetrahydrofolate by a serine hydroxymethyltransferase-glycine complex.