Effect of Hypophysectomy on the Ability of Rat Liver Microsomes in a Cell-free System to incorporate Radioactive Amino-Acids into their Proteins

Abstract

THE incorporation of DL-leucine labelled with carbon-14 into the proteins of a cell-free system¹ prepared from rat liver has been compared with the incorporation obtained under the same conditions with a system prepared in exactly the same way from the livers of hypophysectomized rats. The system was prepared by homogenizing liver in a buffered-sucrose medium¹ and spinning at 14,000g. The unsedimented portion was incubated with the sodium salt of adenosine triphosphate, the sodium salt of creatine phosphate and DL-leucine-1-¹⁴C. The incorporation obtained varied with the experimental conditions used, but in all cases less amino-acid was incorporated into the protein of hypophysectomized rats. The specific activity of the protein from hypophysectomized rats in ten experiments was between 20 and 70 per cent of that found in the normal control system. Treatment of the hypophysectomized rats with growth hormone restored almost to the normal level the ability of the cell-free system to incorporate amino-acids. This in vitro result is compatible with the in vivo observations that hypophysectomy results in a fall in liver weight and protein content and that treatment with growth hormone prevents this fall².