Kinetic studies of adenine phosphoribosyltransferase.

The mechanism of reaction of adenine phosphoribosyltransferase from Ehrlich ascites tumor cells was investigated kinetically by initial velocity and product inhibition studies. The data are consistent with a mechanism in which 5-phosphoribosylpyrophosphate reacts with the enzyme to form an intermediate, presumably an enzyme-ribose 5-phosphate complex, with which adenine then reacts to form adenylate. Noncompetitive inhibition by inorganic pyrophosphate with respect to adenine suggests that the former binds tightly to the enzyme-adenylate complex. Both PP-ribose-P and PPi participate in the form of their magnesium complexes.