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Effect of Amino Acids on Ribosome Aggregation and Protein Synthesis in Perfused Rat Liver^1,2,

Department of Biochemistry and Division of Nutrition, University of Minnesota, St. Paul, Minnesota 55101

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.

KEY WORDS: • polysomes • protein synthesis • liver perfusion • amino acids

¹ Supported in part by National Institutes of Health Grant no. AM 13347-08 and the Minnesota Agricultural Experiment Station. The senior author is grateful for a National Institutes of Health traineeship. This paper is Scientific Journal Series no. 7975, Minnesota Agricultural Experiment Station, University of Minnesota, St. Paul. Minnesota 55101.

² A preliminary report was presented at the 55th annual meeting of the Federation of American Societies for Experimental Biology, 12–17 April, 1971. Chicago, Illinois. Federation Proc. 30: 517 (abstr.). These data are from a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree, University of Minnesota, Minneapolis, 1971.

³ Present address: Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706.

⁴ Present address: Chemistry Department, Illinois State University, Normal, Illinois 61761.

Manuscript received 15 June 1972.