A cyclase is an enzyme, almost always a lyase, that catalyzes a chemical reaction to form a cyclic compound. Important cyclase enzymes include:
- Adenylyl cyclase, which forms cyclic AMP from adenosine triphosphate (EC 4.6.1.1)
- Guanylyl cyclase, which forms cyclic GMP from guanosine triphosphate (EC 4.6.1.2)
- Protein cyclase, a ligase enzyme that produces backbone-cyclised proteins by intramolecular transpeptidation
