title: 31P-NMR study of the orotate phosphoribosyltransferase equilibrium with thiopyrophosphate as substrate.
abstract: 31P-nuclear magnetic resonance spectroscopy was used to directly determine the equilibrium of the reaction catalysed by yeast orotate phosphoribosyltransferase, using orotidine monophosphate and inorganic pyrophosphate as substrates. A Keq value of 0.71 was determined, in good agreement with that of 0.49 calculated by Victor, Greenberg and Sloan (J. Biol. Chem. 254 (1979) 2647-2655), from kinetic data. Substitution of thiopyrophosphate as the substrate shifted the position of the equilibrium 55-fold, to yield a Keq value of 39. Only the beta S analogue of 5-phosphoribosyl 1-diphosphate appeared to be synthesized in this reaction.
mesh_terms: D011756:Diphosphates / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009962:Orotate Phosphoribosyltransferase / Q000378:metabolism*; D010430:Pentosyltransferases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013816:Thermodynamics
chemical_list: D011756:Diphosphates; C046010:monothiopyrophosphoric acid; D010430:Pentosyltransferases; D009962:Orotate Phosphoribosyltransferase