The Mechanism of Guanosine Nucleotide Hydrolysis by p21 c-Ha-ras

Abstract

The use of guanosine 5'-O-(gamma-thio)triphosphate as a substrate for p21 c-Ha-ras was established. By using chirally labeled [gamma-17O,18O]guanosine 5'-O-(gamma-thio)triphosphate, the stereochemical course of the GTPase reaction was determined. The analysis shows that the hydrolysis occurs with inversion at the gamma-phosphorus. This shows that the most likely mechanism is a single step, in-line transfer, without a phosphoenzyme or other phosphorylated intermediate.