Effects of amino acid imbalance on polysome profiles and 14C-labeled amino acid incorporation into tissue proteins in rats.

Feeding of rats on a low casein diet supplemented with a small amount of methionine caused an enlargement of liver size and an accumulation of lipids in the liver. Experiments were conducted to examine the effects induced by the amino acid-imbalanced diet on the metabolism of dietary amino acids with special reference to protein synthesis. Protein and DNA contents of the liver per 100 g body weight with rats fed on the imbalanced diet were apparently higher than those of rats fed on the basal diet. Ingestion of the imbalanced diet clearly stimulated hepatic ribosome aggregation but not skeletal muscle ribosome aggregation. Incorporation of [14C]leucine into liver protein was markedly increased in the group consisting of rats fed on the imbalanced diet (imbalanced group) and that into skeletal muscle was similar to the result with the group receiving the basal diet (basal group). Relative content of [14C]leucine in plasma albumin was higher in rats of the imbalanced group, whereas that in plasma of very low-density lipoprotein was reduced. These results indicate that the unbalanced inter-organ or intra-organ utilizations of dietary amino acids for protein synthesis were produced by the condition of the amino acid imbalance. Such metabolic effects of the amino acid imbalance may result in the enlargement of liver size and the accumulation of lipids in the liver.