L-histidine biosynthesis PMID:17767732 KEGG:map01110 (S)-alpha-Amino-1H-imidazole-4-propionic acid biosynthesis KEGG:map00340 KEGG:map01100 pathway 2-amino-3-(1H-imidazol-4-yl)propanoate biosynthesis PMID:9742729 PMID:16547652 2-amino-3-(1H-imidazol-4-yl)propanoic acid biosynthesis MetaCyc:HISTSYN-PWY PMID:8852895 Biosynthesis of L-histidine, (S)-alpha-Amino- 1H-imidazole-4-propionic acid, a weakly basic amino-acid in a nine- step pathway. Histidine biosynthetic pathway is present in microbes, fungi and plants. Histidine biosynthesis is unusual as a metabolic process utilizing the purine ring of ATP as a carbon and nitrogen source. Histidine biosynthesis pathway is connected to de novo purine biosynthesis pathway through imidazole glycerol phosphate synthase (IGPS) which catalyzes the fifth step and converts N-(5'-phosphoribulosys)-formimino-5-aminoimidazole-4-carboxamide ribonucleotide (PRFAR) to imidazole glycerol phosphate (ImGP) and 5'-(5-aminoimidazole-4-carboxamide) ribonucleotide (AICAR). AICAR is the entry point to the purine biosynthetic pathway. GO:0000105 UPa:UPA00031 amino-acid biosynthesis proteinogenic amino-acid biosynthesis histidine metabolism