Effect of diabetes and insulin treatment on protein synthetic activity of rat liver ribosomes

Abstract

The effect of chronic diabetes and treatment of rats with insulin on the protein synthetic activity of purified rat liver ribosomes was investigated in a cell-free system. 1. 1. The total ribosome population was somewhat inhibited in incorporating activity as a result of diabetes. The free plus bound polysome fraction showed greater differences than the total ribosomes as a result of diabetes while very marked inhibition in activity of the free polysomes was seen after diabetes. These differences were present at all levels of magnesium ion tested (3–20 mM) but tended to disappear at the highest magnesium levels, or if high concentrations of NH 4Cl were present during the preparation of the ribosomes from diabetic rats. 2. 2. These changes in activity were accompanied by marked alterations in polysome profiles. Diabetes resulted in the presence of less polysomes and more dimeric ribosomes. 3. 3. The effects of diabetes and insulin treatment on the activity of ribosomes persists in the presence of 5 · 10 −5 M aurintricarboxylate. 4. 4. The changes which occurred as a result of diabetes could be reversed within 4 h by treatment of diabetic rats with insulin. 5. 5. Ribosomes from diabetic rat liver were more active than normal ones when assayed in the presence of poly(U), especially at magnesium levels at or above the optimal for the poly(U) reaction (10 mM). 6. 6. Ribosomes from diabetic rats are more susceptible to dissociation to subunits by high salt and elevated temperatures than are normal ribosomes.