| 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. |
