Purine nucleoside phosphorylase cleaves the C--O bond of ribose 1-phosphate. Evidence from the 18O shift in 31P NMR.
An equilibrium mixture of highly enriched [18(O)]Pi (represents the mixture of [[18(O)4]Pi, [[18(O)3]Pi, [18(O)2]Pi as represented in the figures, unless otherwise specified), alpha-D-ribose 1-[16(O)]phosphate, and hypoxanthine plus inosine was equilibrated with calf spleen purine-nucleoside phosphorylase (EC 2.4.2.1). The 31P NMR spectrum clearly indicated the formation of alpha-D-ribose 1-[18(O)4]-phosphate and of [16(O)]Pi. Incubation for the same time span in the absence of alpha-D-ribose 1-phosphate left the [18(O)4]Pi isotopic distribution unchanged. The results clearly demonstrated that the C--O bond of alpha-D-ribose 1-phosphate is cleaved in the enzymatic reaction. It is unlikely that the enzyme catalyzes the exchange of oxygen between Pi and H2O. Several possible mechanistic pathways are ruled out by the results, which demand attack by a phosphate oxygen at the anomeric C-1' atom.
D000818:Animals; D002244:Carbon; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D007042:Hypoxanthines; D007288:Inosine; D009682:Magnetic Resonance Spectroscopy; D010100:Oxygen; D010428:Pentosephosphates; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase; D012267:Ribosemonophosphates; D013154:Spleen / Q000201:enzymology
D007042:Hypoxanthines; D010428:Pentosephosphates; D012267:Ribosemonophosphates; D007288:Inosine; D002244:Carbon; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase; D010100:Oxygen