Partial purification of 6-(D-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydropterin triphosphate synthetase from chicken liver.
An enzyme that catalyzes the formation of 6-(D-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydropterin triphosphate (D-erythrodihydroneopterin triphosphate) and formic acid from GTP has been purified about 3700-fold from homogenates of chicken liver. The molecular weight of the enzyme, D-erythrodihydroneopterin triphosphate synthetase (GTP cyclohydrolase), has been estimated to be 125,000 by gel filtration on Ultrogel AcA-34. The enzyme functions optimally between pH 8.0 and 9.2 and is considerably heat-stable. No cofactors or metal ions have been demonstrated to be required for activity; however, the reaction is strongly inhibited by Cu2+ and Hg2+. GTP is the most efficient substrate, with GDP being 1/17 as active and guanosine, GMP, and ATP being inactive. The Km for GTP has been found to be 14 micrometer. Although the overall reaction catalyzed by D-erythrodihydroneopterin triphosphate synthetase from chicken liver is identical with that from Escherichia coli GTP cyclohydrolase, immunological studies show no apparent homology between the two enzymes.
D000619:Aminohydrolases / Q000302:isolation & purification / Q000378:metabolism; D000818:Animals; D001681:Biological Assay; D002645:Chickens; D006136:GTP Cyclohydrolase / Q000302:isolation & purification / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
D000619:Aminohydrolases; D006136:GTP Cyclohydrolase