Purine imidazole ring cyclase

In enzymology, a purine imidazole-ring cyclase (EC 4.3.2.4) is an enzyme that catalyzes the chemical reaction

Hence, this enzyme has one substrate, DNA 4,6-diamino-5-formamidopyrimidine, and two products, DNA adenine and H₂O.

This enzyme belongs to the family of lyases, specifically amidine lyases. The systematic name of this enzyme class is DNA-4,6-diamino-5-formamidopyrimidine C8-N9-lyase (cyclizing DNA-adenine-forming). Other names in common use include DNA-4,6-diamino-5-formamidopyrimidine 8-C,9-N-lyase (cyclizing), DNA-4,6-diamino-5-formamidopyrimidine 8-C,9-N-lyase (cyclizing, and DNA-adenine-forming).