Influence of Alterations in Intracellular Levels of Amino-acids on Protein-synthesizing Activity of Isolated Ribosomes

Abstract

EVIDENCE has been presented which strongly suggests that the rate of protein synthesis in vivo^1,2 and in vitro^3,4 may be very dependent on intracellular concentrations of amino-acids. Of particular significance to the present investigations was the finding that protein turn-over in surviving liver tissue was stimulated in the presence of elevated levels of a single essential ammo-acid^3,4. The catabolic as well as the anabolic phase of protein turnover appeared to be augmented in these circumstances. Interpretation of the results obtained was partially obscured by the fact that intracellular compartmentation of amino-acids may exist, with the result that exogenous and endogenous amino-acids are differentially metabolized^5,6. The experiments recorded here were performed in an attempt to provide definitive data on the influence of cellular levels of amino-acids on the activity of protein-synthesizing systems. The results revealed that the amino-acid incorporating activity of ribosomes isolated from liver slices incubated with a single essential amino-acid varied with the concentration of that amino-acid.