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Aminoacyl Synthetases and Isoaccepting Transfer RNA's from Normal and Regenerating Rat Liver¹

The University of Texas at Houston, M. D. Anderson Hospital and Tumor Institute, Houston, Texas 77025

A detailed investigation of rat liver regeneration and changes in aminoacyl-tRNA synthetase, isoaccepting profiles of tRNA, "tRNA pool" composition, and amino acid pool size has been made for 15 of the common 20 amino acids. An understanding of these changes aids in interpreting phenomena that may play a regulatory role in protein synthesis in rat liver regeneration. Under conditions of maximal acylation, aminoacyl synthetase activities change during regeneration, but not synchronously. By contrast, the tRNA composition of the effective tRNA pool remains constant. That is, the proportion of tRNA that will accept a given amino acid remains a constant part of the total acceptor activity. Similarly, the isoacceptor profiles of tRNA from normal and regenerating liver are identical. No differences were noted in the assay conditions for maximal acylation for aminoacyl synthetases derived from livers after sham operation, or at 12, 18, or 24 hr posthepatectomy. There is a general increase in the amounts of extractable amino acids during regeneration. The concentrations of amino acids found in vivo are higher than the concentrations of amino acids necessary for optimal activity in vitro.

¹ Supported by American Cancer Society Grant P-501D and the Robert A. Welch Foundation Grants G-035 and G-415.

² American Cancer Society Professor of Biochemistry.

Received 11/11/71. Accepted 2/11/72.