Inhibition of Insulin Degradation by Nonsuppressible Insulin-Like Activity

vided by three sources, was evaluated for its effect on the proteolytic degradation of insulin utilizing insulin protease obtained from rat liver homogenate as well as liver cell membranes. All three preparations of nonsup-pressible insulin-like activity were found to be competi-tive inhibitors of insulin degradation. In addition human plasma was fractionated yielding an acetone precipitate which was found to have nonsup-pressible insulin-like activity and to be a competitive in-hibitor of insulin protease