ID 4.3.2.4 DE purine imidazole-ring cyclase. CA DNA 4,6-diamino-5-formamidopyrimidine = DNA adenine + H2O. CC -!- Also acts on 2,6-diamino-5-formamido-3,4-dihydro-4-oxopyrimidine CC residues. CC -!- Brings about the reclosure of the imidazole rings of purine residues CC damaged by gamma-rays. //