EFFECT OF MG2+ ON SOME PROPERTIES OF NUCLEOTIDE-FREE ELONGATION-FACTOR TU FROM BACILLUS-STEAROTHERMOPHILUS

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. Copyright © 1979, Wiley Blackwell. All rights reserved