Leucyl‐tRNA and Aarginvl‐tRNA Synthetases of Wheat Germ

Abstract

Leucyl‐tRNA and arginyl‐tRNA synthetases were purified from wheat embrovos by the following purification steps: ammonium sulfate precipitation, gel filtration on Sephadex G‐75, chromatogrphies on DEAE‐cellulose and hydroxyapatite, and finally gel electrophoresis. The molecular weights of these enzymes were found to be about 110000 for leucyl‐tRNA synthetase and 70000 for arginyl‐tRNA synthetase. Their structures, deduced by dodecylsufate electrophoresis after reducing treatment, were found to be dimeric for the former and monomeic for the latter. Leucyl‐tRNA synthetase exhibits an equilibrium between an active dimeric formand an inactive monomeric form. The number of subunits was determined at dissociation equilibrium by relations deducd from the law of mass action and modified for olighomeric enzymes. When the instantaneous modifications of the activity of these two synthetases are studied in the presence of rebosomes, both activities are slightly stimulated. In addition, when ribosomes (or bovine serum albumin) are preincubated together with the two synthetases, they reduce both the inactivation by dissociation of leucyl‐tRNA synthetase and the inactivation (probably by isomerization) of arginyl‐tRNA synthetase. Although the ribosomes and bovine serum albumin have apparently similar effects, the great difference in effective concention between the two, ∼ 1 nM for ribosomes and 30 μM for bovine serum albumin, that the ribosome have a certain specificity of activn; this may involve the maintenance of the synthetases in their conformationally active state.