In eukaryotes, occurs as a trifunctional enzyme also having methenyltetrahydrofolate cyclohydrolase (EC
3.5.4.9) and formate---tetrahydrofolate ligase (EC
6.3.4.3) activity. In some prokaryotes occurs as a bifunctional enzyme also having methenyltetrahydrofolate cyclohydrolase activity (EC
3.5.4.9).