In enzymology, a methenyltetrahydrofolate cyclohydrolase () is an enzyme that catalyzes the chemical reaction 5,10-methenyltetrahydrofolate + H2O 10-formyltetrahydrofolate Thus, the two substrates of this enzyme are 5,10-methenyltetrahydrofolate and H2O, whereas its product is 10-formyltetrahydrofolate. This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in cyclic amidines. This enzyme participates in glyoxylate and dicarboxylate metabolism and one carbon pool by folate. Synonyms The systematic name of this enzyme class is 5,10-methenyltetrahydrofolate 5-hydrolase (decyclizing). Other names in common use include: Citrovorum factor cyclodehydrase cyclohydrolase formyl-methenyl-methylenetetrahydrofolate synthetase (combined). Structural studies As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes , , , , , and . References EC 3.5.4 Enzymes of known structure