Ternary Complex Formation between Elongation Factor Tu, GTP and Aminoacyl-tRNA: an Equilibrium Study

Abstract

The equilibria between the elongation factor Tu · GTP complex (EF‐Tu · GTP) from Escherichia coli and tyrosyl‐tRNA^Tyr from E. coli as well as phenylalanyl‐tRNA^Phe and seryl‐tRNA^Ser from yeast were studied using a novel procedure, which takes advantage of the protective effect of ternary complex formation on the stability of the aminoacyl bond against non‐enzymatic hydrolysis. At 25 °C and at pH 7.4 tyrosyl‐tRNA^Tyr, phenylalanyl‐tRNA^Phe and seryl‐tRNA^Ser are bound with binding constants of 0.7 × 10⁷ M⁻¹, 5.0 × 10⁷ M⁻¹ and 0.5 × 10⁷ M⁻¹ respectively. The binding of aminoacyl‐tRNA to EF‐Tu · GTP has a negative ΔH of the order of 10 kcal/mol (42 kJ mol). Complex formation is dependent on ionic strength: with 0.1 M KCl K_ass= 0.5 × 10⁷ M⁻¹, with 0.5 M KCl K_ass= 0.2 × 10⁷ M⁻¹ was determined for the binding of Tyr‐tRNA^Tyr.