title: GTP-cyclohydrolases: a review.
abstract: The occurrence, properties and functions of GTP-cyclohydrolases in mammalian and non-mammalian systems is reviewed. GTP-cyclohydrolases catalyse the removal of C-8 atom from GTP as formic acid. GTP-cyclohydrolase I (EC 3.5.4.16) converts GTP into D-erythro-7, 8-dihydroneopterin triphosphate, whereas GTP-cyclohydrolase II forms 2,5-diamino-4-oxo-6-(5'-phosphoribosyl) -amino pyrimidine, a possible intermediate in the biosynthesis of riboflavin. GTP-cyclohydrolase I is the first enzyme in the biosynthesis of tetrahydrobiopterin, a cofactor of the monooxygenases of the aromatic amino acids. It is the rate limiting enzyme in many mammals, but not in man. Recently, patients with GTP -cyclohydrolase I deficiency were described, a variant form of tetrahydrobiopterin-deficient hyperphenylalaninaemia.
mesh_terms: D000619:Aminohydrolases / Q000378:metabolism*; D000818:Animals; D001419:Bacteria / Q000201:enzymology; D001708:Biopterins / Q000031:analogs & derivatives / Q000096:biosynthesis; D055598:Chemical Phenomena; D002621:Chemistry; D002848:Chromatography, DEAE-Cellulose; D005492:Folic Acid / Q000096:biosynthesis; D006136:GTP Cyclohydrolase / Q000172:deficiency / Q000302:isolation & purification / Q000378:metabolism*; D006728:Hormones / Q000502:physiology; D008099:Liver / Q000201:enzymology; D008970:Molecular Weight; D013045:Species Specificity
chemical_list: D006728:Hormones; D001708:Biopterins; D005492:Folic Acid; D000619:Aminohydrolases; D006136:GTP Cyclohydrolase; C003402:sapropterin