Effects of supplementation and depletion of a single essential amino acid on hepatic polyribosome profile in rats.

The effects of supplementation and depletion of one essential amino acid on hepatic polysome profile of rats were investigated in the meal-feeding condition. Only methionine supplementation to a protein-free diet reduced the population of monosomes and disomes per total profile. The single supplementation of other essential amino acids did not change the polysome profile as compared with the protein-free diet group. The results suggested that, when rats were fed a protein-free diet, methionine is the first limiting amino acid for liver protein synthesis. In the case of depletion of one essential amino acid (tryptophan, methionine-cystine, threonine, phenylalanine-tyrosine, leucine, isoleucine, valine, lysine), the values of monosomes and disomes per total ribosomes of rats were significantly higher than that of rats fed a complete amino acid mixture diet. In rats tube-fed the threonone-deficient diet three times a day for 3 or 5 days, the polysomes in liver were aggregated heavier than those of rats that received a complete diet. These results indicated that, under meal-feeding condition which may be considered more a physiological condition than force-feeding, the deficiency of single essential amino acid generally causes the disaggregation of hepatic polysomes leading the decreased synthesis of hepatic proteins.