Kinetic studies of hypoxanthine-guanine phosphoribosyltransferase.

The mechanism of reaction of human erythrocyte hypoxanthine-guanine phosphoribosyltransferase was investigated by initial velocity, product inhibition, and isotope exchange studies. Although initial velocity data are compatible with a mechanism involving binary enzyme-substrate complexes, the product inhibition and isotope exchange studies indicate that the reaction is ordered with the formation of ternary enzyme-substrate complexes. Product and alternative product inhibition data, alternative substrate inhibition experiments, and combined alternative substrate initial velocity data are all consistent with the view that only one enzyme catalyzes this reaction of hypoxanthine and guanine, and that they share a common binding site.