The effect of hypophysectomy of the rat and of treatment with growth hormone on the incorporation of amino acids into liver proteins in a cell-free system

Publisher Website
Google Scholar
Abstract
Less radioactive amino acid was incorporated into protein in vitro in a cell-free system (Zamecnik and Keller, 1954) prepared from the livers of hypophysectomized rats than from the livers of normal rats. Changes in the activity of the amino acid-activating enzymes of the soluble fraction of the cell or in the ability of the soluble ribonucleic acid (RNA) to form amino acid-soluble RNA intermediates were not responsible for the diminished incorporation resulting from hypophysectomy. The microsomes from the livers of hypophysectomized rats were, however, less able than those from normal rats'' liver to incorporate the activated amino acids into protein. This diminished ability could not be attributed to (a) greater breakdown of the microsomes during incubation by more extensive ribonuclease or proteolytic-enzyme activity, (b) differences in the optimum conditions needed by the preparations from differently treated rats, or (c) the smaller food intake of the hypophysectomized than of normal rats. Starvation of normal or of hypophysectomized rats for 18 hr. did not alter the ability of the liver microsomes to incorporate amino acids into protein, nor was incorporation in this system related to the glycogen content of the liver. Treatment of the hypophysectomized rats with ox growth hormone restored in part, the ability of their liver microsomes to incorporate amino acids into protein. Other pituitary hormones may also be concerned. Treatment of normal rats with growth hormone increased the ability of the liver microsomes to incorporate amino acid into protein. The depressed rate of protein biosynthesis observed in vivo in the livers of hypophysectomized rats may thus be partly accounted for.