Effect of insulin and glucose on the activity of insulin-degrading enzymes in rat liver.

The degradation of insulin by insulin protease and glutathion-insulin transhydrogenase (glutathioneproteindisulphide oxidoreductase--EC 1.8.4.2, GIT) was measured in rat liver either after replacing food and water by 15% glucose solution, or after daily insulin administration 8 U daily for 3 days or after fasting. The breakdown of radioiodinated insulin was followed by measuring the increase of TCA soluble radioactivity during incubation of cell fractions with 125I insulin at 37 degrees C. The highest GIT activity was observed in liver microsomes of rats after glucose feeding and after insulin administration, whereas enzyme activity of fasted animals did not essentially differ from corresponding values of normally fed controls. The insulin protease in cytosol of liver cells remained unchanged after these procedures. The important role of GIT in insulin degradation seems to be conclusively demonstrated.