title: Phosphorolytic and ribosyl transfer mechanisms of purified chicken liver purine nucleoside phosphorylase.
abstract: Purified chicken liver purine nucleoside phosphorylase shows two ionizable groups at the active site whose pKa were near pH 6.9 and 8; the molecular weight (67,000-89,000) depends on the protein concentration. Initial velocity studies and product inhibition patterns were consistent with a random mechanism, which is rapid equilibrium in the phosphorolytic reaction with a dead-end complex, but not in the synthetic reaction. Free inorganic orthophosphate purine nucleoside phosphorylase (Sephadex G-100) catalyzes a pentosyl transfer reaction from inosine to guanine according to a random Bi, Bi mechanism.
mesh_terms: D000818:Animals; D002645:Chickens; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D010430:Pentosyltransferases / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology; D011683:Purine-Nucleoside Phosphorylase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D010710:Phosphates; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase