title: The application of 8-aminoguanosine triphosphate, a new inhibitor of GTP cyclohydrolase I, to the purification of the enzyme from human liver.
abstract: GTP cyclohydrolase I from human liver and Escherichia coli is competitively inhibited by 8-aminoguanosine triphosphate with a dissociation constant (Ki) of 0.25 mumol/l. 8-Aminoguanosine triphosphate, prepared from GTP and hydroxylamine-O-sulfonic acid, was coupled to Sepharose 4B and used as an affinity adsorbent for a 309-fold purification of GTP cyclohydrolase I from human liver. GTP cyclohydrolase I from human liver is a relatively heat-stable enzyme with a half-life of 2 min at 80 degrees C, an isoelectric point (pI) of about 5.6, and a Km for GTP of 31 mumol/l. Addition of KCl (0.3 mol/l) increased the Km to 153 mumol/l. No cofactors were required for activity. L-erythro-5,6,7,8-Tetrahydrobiopterin, L-erythro-7,8-dihydrobiopterin, L-sepiapterin and 8-aminoguanosine triphosphate were strong inhibitors.
mesh_terms: D000619:Aminohydrolases / Q000302:isolation & purification*; D002846:Chromatography, Affinity / Q000379:methods; D006136:GTP Cyclohydrolase / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D008099:Liver / Q000201:enzymology*
chemical_list: C047842:8-aminoguanosine triphosphate; D006160:Guanosine Triphosphate; D000619:Aminohydrolases; D006136:GTP Cyclohydrolase