Studies on the Incorporation of Amino Acids by a Cell-Free System Obtained from Beef Retina

Abstract

The incorporation of 14C-leucine into proteins by a cell-free system from beef retina was studied. It was found that the optimum concentration of ATP depended on the concentration of ribosomes in the incubation medium. Very little incorporation of 14C-leucine was observed in the absence of K+. The optimum concentration of phosphocreatine required for incorporation of radioactive leucine depended on the concentration of Mg2+ in the incubation medium, and the optimum concentration of K+ appears to be independent of the concentrations of Mg2+ and phosphocreatine used.Retinol and retinal had no effect, but ethanol markedly inhibited protein synthesis at concentrations higher than 2%.Puromycin (10−4 M) inhibited incorporation of 14C-leucine by about 80%. The degree of inhibition by cycloheximide depended on the concentration of pH 5 fraction in the incubation medium.