The Effect of Mg2+ on Some Properties of Nucleotide‐Free Elongation Factor Tu from Bacillus stearothermophilus

Abstract

The nucleotide-free elongation factor from Bacillus stearothermophilus provides a means to study the effect of Mg²⁺ ions on various reactions of the protein. The binding of GDP to the protein is stimulated by Mg²⁺. From comparative studies with other metal ions, particularly Mn²⁺, it appears that this stimulation is due to the formation of a metal · GDP complex which is bound to the protein. Protection against proteolysis by trypsin is afforded by both Mg²⁺ and Mg · GDP, but not by GDP alone. The rate of substitution of the sulphydryl group associated with aminoacyl-tRNA binding, by either 5,5′-dithio-bis(2-nitrobenzoic acid) or N-ethylmaleimide is reduced in the presence of Mg²⁺. All these observations show that Mg²⁺ not only is involved in GDP binding but also has a direct effect on the tertiary structure of the protein.