Effect of Amino Acids on Ribosome Aggregation and Protein Synthesis in Perfused Rat Liver

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Abstract
To study the effects of amino acids on the degree of ribosomal aggregation and the capacity for amino acid incorporation into protein, isolated livers from fasted, male rats were perfused in situ with washed rat erythrocytes suspended in Ringer's bicarbonate buffer containing bovine serum albumin. Perfusion for 1 hour resulted in a decrease in heavy ribosome aggregates and an increase in ribosomes, free of messenger RNA. Addition to the 50 ml perfusate of a mixture of 20 amino acids at normal plasma levels and infusion of this amount each 15 minutes were sufficient to maintain polysomes and subsequent in vitro amino acid incorporation at the postsurgery levels. Perfusion with twice normal levels of amino acids resulted in formation of polysomes, whereas perfusion with one-half normal levels resulted in loss of polysomes. Omission of tryptophan or methionine from the amino acid mixture resulted in disaggregation of polysomes and decreased ability to incorporate amino acids in vitro. With the deficient infusion mixture, an initial concentration of 15 μg/ml tryptophan or 36 μg/ml methionine was necessary to prevent disaggregation of polysomes and a decrease in the capacity for subsequent in vitro amino acid incorporation.