Effect of dietary amino acids on transfer ribonucleic acid charging levels in rat liver.

In order to examine the mechanism of the effect of dietary amino acids on hepatic polysome aggregation and protein synthesis, tRNA charging levels (tRNA acylated with amino acids) were measured in the livers of rats meal-fed (trained to eat for 2 hours/day) a 15% casein diet at the high and low point of polysome aggregation, and of meal-fed and control-fed (ad libitum feeding from 1800 to 0800 hours) rats fed an isoleucine deficient diet. The charging levels of tRNAs for two of the amino acids tested, namely isoleucine and phenylalanine, did not drop with the diurnal changes that occur in polysome aggregation, whereas, the feeding of an isoleucine deficient diet resulted in a 25% decrease in the ile-tRNA charging levels. Although it is not clear how amino acid supply regulates polysome aggregation and protein synthesis, it would not appear to be mediated via a decrease in tRNA charging levels.