The kinetic mechanism of the release of nucleotide from elongation factor Tu promoted by elongation factor Ts determined by pressure relaxation studies.

The release of a chromophoric analogue of GDP, 2-amino-6-mercaptopurine riboside 5'-diphosphate (thioGDP), from its complex with elongation factor Tu (EF-Tu) is catalyzed by elongation factor Ts (EF-Ts). The mechanism of this reaction includes a ternary complex; EF-Tu.thioGDP.EF-Ts (Eccleston, J. F. (1984) J. Biol. Chem. 259, 12997-13003). This mechanism has been further investigated using pressure relaxation techniques combined with spectrophotometric measurements. The equilibrium of a solution of EF-Tu, EF-Ts, and thioGDP over a range of concentrations is perturbed on increasing the pressure to 150 atm. Rapid decrease of the pressure back to 1 atm results in a biphasic relaxation process, an initial fast phase which is complete within 1 ms followed by a slower phase. This is interpreted as the result of an isomerization of the EF-Tu.thioGDP.EF-Ts ternary complex which occurs before the release of thioGDP. Such an isomerization process may be a general feature in the release of GDP from guanosine nucleotide-binding proteins.