A Possible Role for Ribonuclease in the Regulation of Protein Synthesis in Normal and Hypophysectomized Rats

Abstract

Abstract Postmitochondrial supernatant fractions derived from livers of hypophysectomized rats were found to contain twice the level of total (active + latent) alkaline RNase found in similar preparations from normal animals. Polysomes isolated from both sources often had similar optical density profiles, and both supported amino acid incorporation in vitro to about the same extent. Occasionally, however, polysomes obtained from hypophysectomized rats were of a smaller size class distribution than preparations from normal animals, and these preparations exhibited a correspondingly decreased capacity to support cell-free protein synthesis. This breakdown of polysomes was associated with an increase in the active RNase content of the corresponding postmitochondrial supernatant fraction. It is suggested that the apparent translational defect, reported by others, of polysomes isolated from livers of hypophysectomized rats may result from the effect of RNase upon polysomes during isolation and subsequent incubation. The elevated RNase levels of postmitochondrial supernatant fractions obtained from hypophysectomized animals were reduced to normal levels by intraperitoneal injection of bovine growth hormone, and optical density profiles and protein-synthesizing capacity of polysomes obtained from growth hormone-treated hypophysectomized rats were comparable to those of normal preparations.