Decreased protein synthesis by polysomes, tRNA and aminoacyl-tRNA synthetases isolated from senescent rat liver.

A cell-free in vitro protein-synthesizing system isolated from adult(10-13-month) and senescent(24-30-month) female Wistar rat liver is described. Optimal concentrations of polysomes, aminoacyl-tRNA synthetases, tRNA, Mg 2+, K+, and labeled amino acids are reported for this in vitro system. Both are rate and extent of protein synthesis are lower with the system from senescent liver compared to that from adult liver. Senescent polysomes, tRNA synthetases, and tRNA all contribute to this decrease. Free adult or senescent polysomes support protein synthesis to the same extent. However, compared to adult polysomes, senescent membrane-bound polysomes support less protein synthesis and account for an increased proportion of the total polysome fraction. Ribonuclease and protease activities are low in the adult and the senescent in vitro systems and do not account for the decreased protein synthesis with the latter.