Protein synthesis studies in skeletal muscle of aging rats. I. Alterations in nitrogen composition and protein synthesis using a crude polyribosome and pH 5 enzyme system.

The effect of aging on rat skeletal muscle protein synthesis was studied using a cell-free system. The activity of crude polyribosomes from hind-limb skeletal muscle was reduced by 40% in aged animals (22 to 24 months) and by 20% in the mature (12 months) animal compared with young (2 month) rats. In a poly Uridylic-acid-directed incorporation system the ribosomes from aged and mature animals showed a decrease in activity. Sucrose density gradient analysis also demonstrated a loss of heavy polyribosomes in aged and mature animals. The pH 5 enzyme fraction from aged and mature animals was less efficient than that from young rats in support of protein synthesis, suggesting a decreased activity of soluble factors. In conclusion, aging leads to a progressive decline in the efficiency of protein synthesis, associated with both the ribosome and soluble fractions of the cell.