ACTIVATION AND INHIBITION OF INSULIN-RECEPTOR AUTOPHOSPHORYLATION BY TRYPSIN TREATMENT OF INTACT H35 CELLS

1. Treatment of intact cultured H35 cells with trypsin (1 mg/ml) for 1 5 min at low temperature (4-degrees-C) or for 30 sec at 37-degrees-C c auses activation of the insulin receptor subsequently isolated from th e cells. 2. Receptor activation was assessed by increased phosphotyros ine content of the beta-subunit of the receptor, and increased autopho sphorylation using [P-32]-ATP. 3. Treatment of the cells for 15 min at 37-degrees-C however completely abolished insulin binding and all ins ulin receptor kinase activity. 4. These data demonstrate that proteoly tic damage of the extracellular domain of the insulin receptor can ren der the receptor kinase inactive and lead to a cell which is unrespons ive to insulin.