Transition state structures and the roles of catalytic residues in GAP-facilitated GTPase of Ras as elucidated by (18)O kinetic isotope effects.

ABSTRACT: Ras-catalyzed guanosine 5' triphosphate (GTP) hydrolysis proceeds through a loose transition state as suggested in our previous study of (18)O kinetic isotope effects (KIE) [ Du , X. et al. ( 2004 ) Proc. Natl. Acad. Sci. U.S.A. 101 , 8858 - 8863 ]. To probe the mechanisms of GTPase activation protein (GAP)-facilitated GTP hydrolysis reactions, we measured the (18)O KIEs in GTP hydrolysis catalyzed by Ras in the presence of GAP(334) or NF1(333), the catalytic fragment of p120GAP or NF1. The KIEs in the leaving group oxygens (the beta nonbridge and the beta-gamma bridge oxygens) reveal that chemistry is rate-limiting in GAP(334)-facilitated GTP hydrolysis but only partially rate-limiting in the NF1(333)-facilitated GTP hydrolysis reaction. The KIEs in the gamma nonbridge oxygens and the lea

SUBMITTER: Du X 

PROVIDER: S-EPMC3862183 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature