InterPro domain: IPR006062

Histidine is formed by several complex and distinct biochemical reactions catalysed by eight enzymes. Proteins involved in steps 4 and 6 of the histidine biosynthesis pathway are contained in one family. These enzymes are called His6 and His7 in eukaryotes and HisA and HisF in prokaryotes. HisA is a phosphoribosylformimino-5-aminoimidazole carboxamide ribotide isomerase ( 5.3.1.16 ), involved in the fourth step of histidine biosynthesis. The bacterial HisF protein is a cyclase which catalyses the cyclization reaction that produces D-erythro-imidazole glycerol phosphate during the sixth step of histidine biosynthesis. The yeast His7 protein is a bifunctional protein which catalyses an amido-transferase reaction that generates imidazole-glycerol phosphate and 5-aminoimidazol-4-carboxamide. The latter is the ribonucleotide used for purine biosynthesis. The enzyme also catalyses the cyclization reaction that produces D-erythro-imidazole glycerol phosphate, and is involved in the fifth and sixth steps in histidine biosynthesis.