title: Guanosine triphosphate cyclohydrolase activity in rat tissues.
abstract: The GTP cyclohydrolase activity of rat tissues has been studied by means of the measurement of formic acid release and neopterin synthesis from GTP. After gel filtration of a 45%-satd.-(NH4)2SO4 fraction of liver homogenates, three enzyme fractions were separated and named A1, A2 and A3 according to the order of their elution. Fractions A1 and A3 displayed an 8-formyl-GTP deformylase activity; no proof of cyclized product has yet been established. This activity was heat-labile and required Mg2+ for maximal activity. Fraction A2 displayed a 'neopterin-synthetase' activity, with dihydroneopterin triphosphate and formic acid formed in stochiometric amounts. Fraction A1 isolated from heat-treated homogenates also produced dihydroneopterin triphosphate. Neopterin synthetase activity in fractions A1 and A2 was heat-resistant and inhibited by Mg2+. In liver the A2 fraction represented 70-75% of the neopterin synthetase capacity and was inhibited by reduced pterines (sepiapterin, dihydrobiopterin and tetrahydrobiopterin) and to a lesser extent by reduced forms of folic acid. In kidney and brain, fraction A1 and A3 GTP 8-formylhydrolase activities were found in significant amounts, in contrast with the neopterin synthetase activity, which was low and appeared to be confined to the A1 fraction.
mesh_terms: D000619:Aminohydrolases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology; D002850:Chromatography, Gel; D005561:Formates / Q000378:metabolism; D006136:GTP Cyclohydrolase / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D008297:Male; D008956:Models, Chemical; D019798:Neopterin / Q000031:analogs & derivatives; D011621:Pteridines / Q000096:biosynthesis / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014018:Tissue Distribution
chemical_list: D005561:Formates; D011621:Pteridines; C030544:formic acid; C013490:dihydroneopterin triphosphate; D019798:Neopterin; D000619:Aminohydrolases; D006136:GTP Cyclohydrolase