cd04731

The cyclase subunit of imidazoleglycerol phosphate synthase (HisF). Imidazole glycerol phosphate synthase (IGPS) catalyzes the fifth step of histidine biosynthesis, the formation of the imidazole ring. IGPS converts N1-(5'-phosphoribulosyl)-formimino-5-aminoimidazole-4-carboxamide ribonucleotide (PRFAR) to imidazole glycerol phosphate (ImGP) and 5'-(5-aminoimidazole-4-carboxamide) ribonucleotide (AICAR). This conversion involves two tightly coupled reactions in distinct active sites of IGPS. The two catalytic domains can be fused, like in fungi and plants, or peformed by a heterodimer (HisH-glutaminase and HisF-cyclase), like in bacteria.