Abstract
The present study demonstrated that at physiological concentrations of insulin bacitracin inhibited the degradation of specifically bound insulin by enzymes located in the rat adipocyte plasma membrane. Bacitracin increased the amount of intact insulin specifically bound to the plasma membrane and potentiated the stimulation of adipocyte glucose oxidation by submaximal concentrations of the hormone. In contrast to agents such as chloroquine, which inhibit lysosomal degradation of internalized insulin, bacitracin was shown by two approaches to inhibit a degradative process localized to the adipocyte plasma membrane. Cyanide and 2,4-dinitrophenol, agents which inhibit energy requiring endocytosis, had no effect on the bacitracin inhibition of cellular degradation of 125I-insulin. Bacitracin directly inhibited 125I-insulin degradation by isolated plasma membranes at similar concentrations and to a similar extent as found with cells. The degradative process inhibited by bacitracin accounted for the majority of cellular degradation of the hormone. The increased 125I-insulin bound to adipocytes was shown to be intact by gel chromatographic analysis and was localized to the plasma membrane by direct and indirect approaches. Bacitracin increased 125I-insulin specifically bound to isolated plasma membranes as early as 2 min. The 125I-insulin bound to adipocytes in the presence of bacitracin was completely dissociable by the addition of 8 microM unlabeled insulin whereas a significant portion of 125I-insulin bound to chloroquine-treated cells could not be dissociated. Bacitracin slowed dissociation of 125I-insulin from the cells. Bacitracin increased the 125I-insulin binding to cells in the presence and absence of cyanide and 2,4-dinitrophenol. Bacitracin potentiated the stimulation of adipocyte glucose oxidation at submaximal concentrations of insulin.
Highlights
The present study demonstratetdhat apt hysiological concentrations of insulin bacitracin inhibited the degradation of bound insulin by enzymes located in the rat adipocyte plasma membrane
Bacitracip increased the amount of intact insulin bound to the plasma membrane and potentiated the stimulation of adipocyte glucose oxidation by submaximal concentrations of the hormone
Incontrastto agents such as chloroquine, which inhibit lysosomal degradation of internalized insulin, bacitracinwas shown by two approachesto inhibit a degradative process localized to the adipocyte plasma membrane
Summary
The present study demonstratetdhat apt hysiological concentrations of insulin bacitracin inhibited the degradation of bound insulin by enzymes located in the rat adipocyte plasma membrane. Bacitracip increased the amount of intact insulin bound to the plasma membrane and potentiated the stimulation of adipocyte glucose oxidation by submaximal concentrations of the hormone Incontrastto agents such as chloroquine, which inhibit lysosomal degradation of internalized insulin, bacitracinwas shown by two approachesto inhibit a degradative process localized to the adipocyte plasma membrane. Bacitracin caused anincrease in bound intact insulin on the plasma membrane, a decrease in the insulin dissociation rate, and potentiationof the stimulation of glucose oxidation by submaximal concentrations of insulin These results are consistent witha model of insulin action in which control of occupancy of the insulin receptor by plasma membrane degradationof the bound insulin helps regulate the membrane evewnhtsich may trigger the generationof an insulin chemical mediator
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have