. "Catalysis of the reaction: 5,10-methenyltetrahydrofolate + H2O = 10-formyltetrahydrofolate." . . "methenyltetrahydrofolate cyclohydrolase activity" . "5,10-methenyl-THF cyclohydrolase activity" . "5,10-methenyltetrahydrofolate 5-hydrolase (decyclizing)" . "citrovorum factor cyclodehydrase activity" . "formyl-methenyl-methylenetetrahydrofolate synthetase (combined)" . . .