THE PRESENCE OF INSULIN-DEGRADING ENZYME IN HUMAN ILEAL AND COLONIC MUCOSAL CELLS

The aim of this research is to characterize the presence of insulin-de grading enzyme in human colon and ileal mucosal cells. Biochemical stu dies, including the activity-pH profiles, the effects of enzyme inhibi tors, immunoprecipitation and western blots, were conducted. The major ity of insulin-degrading activity in colon mucosal cells was localized in the cytosol. In both colon and ileum, cytosolic insulin-degrading activities had a pH optimum at pH 7.5, and were extensively inhibited by each of N-ethylmaleimide, p-chloromercuribenzoate, and 1,10-phenant hroline, but were very weakly affected by each of leupeptin, chymostat in, diisopropyl phosphofluoridate and soybean trypsin inhibitor. In th e colon and ileum, more than 93% and 96%, respectively, of cytosolic i nsulin-degrading activities were removed by the mouse monoclonal antib ody to human RBC insulin-degrading enzyme, as compared with less than 20% by the normal mouse IgG for both tissues. Further, a western blot analysis revealed that a cytosolic protein of 110 kD, in both human co lon and ileum, reacted with the monoclonal antibody to insulin-degradi ng enzyme. It is concluded that insulin-degrading enzyme is present in the cytosol of human colon and ileal mucosal cells.