Dipeptide metalloendoprotease substrates are glucose transport inhibitors and membrane structure perturbants

Abstract

Dipeptide substrates for metalloendoproteases have previously been shown to block biological processes requiring membrane fusion. Thus, we employed such compounds as potential inhibitors of the insulin-dependent activation of glucose transport in fat cells. This event is thought to involve vesicle movement from an intracellular site to the cell surface and would therefore require membrane fusion during the activation step. We find that synthetic dipeptides which are metalloendoprotease substrates rapidly and reversibly inhibit insulin-activated glucose oxidation in a dose-dependent manner but exhibit essentially no effect on basal levels. A similar result is obtained when glucose transport is measured directly in intact fat cells, in metabolically poisoned cells, and in isolated membrane vesicles derived from insulin-activated or untreated fat cells. That is, the dipeptide substrates inhibit insulin-activated glucose uptake to a greater extent than basal transport, and they do so even when vesicle translocation and fusion have already taken place as in ATP-depleted cells and isolated vesicles. Onset of transport inhibition after dipeptide addition is rapid, but not instantaneous, with a t 1/2 of 15-30 s. The metalloendoprotease substrates also inhibit glucose uptake and cytochalasin B binding in human erythrocytes but not in human placental microsomes. Finally, light microscopic examination of substrate-treated red cells reveals marked cupping and/or echinolation of the cell membrane. We conclude the following from these observations: Metalloendoprotease substrates are inhibitors of adipocyte glucose transport.