title: A study of the kinetic mechanism of elongation factor Ts.
abstract: Elongation factor Ts (EF-Ts) catalyzes the reaction EF-Tu X GDP + nucleotide diphosphate (NDP) reversible EF-Tu X NDP + GDP where NDP is GDP, IDP, GTP, or GMP X PCP. The EF-Ts-catalyzed exchange rates were measured at a series of concentrations of EF-Tu X [3H] GDP and free nucleotide. Plotting the rate data according to the Hanes method produced a series of lines intersecting on the ordinate, a characteristic of substituted enzyme mechanisms. GDP is a competitive inhibitor of IDP exchange, a result predicted for the substituted enzyme mechanism but inconsistent with ternary complex mechanisms that involve an intermediate complex containing EF-Ts and both substrates. The exchange of both GTP and the GTP analog GMP X PCP also follow the substituted enzyme mechanism. The maximal rates of exchange of GDP and GTP are the same, which indicates that the rates of dissociation of EF-Ts from EF-Tu X GDP and EF-Tu X GTP are the same. The steady-state maximal exchange rate is slower by a factor of 20 than the previously reported rate of dissociation of GDP from EF-Ts X EF-Tu. This is interpreted to mean that the rate-determining step in the exchange reaction is the dissociation of EF-Ts from EF-Tu X GDP.
mesh_terms: D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D007290:Inosine Diphosphate; D007700:Kinetics; D010445:Peptide Elongation Factors; D013696:Temperature
chemical_list: D010445:Peptide Elongation Factors; C023512:elongation factor Ts; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D007290:Inosine Diphosphate