REGULATION OF MULTICATALYTIC ENZYME-ACTIVITY BY INSULIN AND THE INSULIN AND THE INSULIN-DEGRADING ENZYME

The insulin-degrading enzyme (IDE) plays an important role in the cell ular metabolism of insulin. Recent studies have also suggested a regul atory role for this protein in controlling the activity of cytoplasmic protein complexes, including the proteasome [multicatalytic proteinas e (MCP)] and the glucocorticoid and androgen receptors. Binding of IDE to these complexes increases their activity, whereas the addition of substrates for IDE inhibits activity. This provides a potential mechan ism of action for internalized insulin and other IDE substrates in the control of protein turnover. To examine further the interactions, par tially purified IDE-MCP complex was treated with EDTA. or EGTA, and ac tivity was measured in the absence and presence of various divalent ca tions (Ca2+, Mn2+, Co2+, and Zn2+) and insulin. EDTA treatment reduced MCP activity and eliminated the effect of insulin on the complex. Div alent cations partially or completely restored MCP activity, but did n ot restore the effect of insulin. EGTA treatment had a lesser effect o n MCP activity, but abolished insulin inhibition of activity. Divalent cations restored the insulin effect. Inhibitors of IDE also blocked t he insulin effect on MCP activity, as did treatment with SDS. These fi ndings suggest that conformational changes in the complex may play a r ole in the insulin control of MCP activity.