Influence of individual amino acids on incorporation of [14C]leucine by rat liver ribosomes.

The report of Baliga et al. (1) that the nutritionally essential amino acids promote initiation of protein synthesis by isolated rat liver ribosomes has been reinvestigated. We were unable to observe any particular influence of essential amino acids on the incorporation of leucine into protein. We find instead that glutamine, glutamate, asparagine and aspartate appear to exert a greater influence than the essential amino acids on leucine incorporation by the ribosomes and suggest that the availability of amino acids in cell-free systems primarily affects elongation.