Insulin-degrading enzyme hydrolyzes ATP.

Abstract

We reported in a previous work that insulin degradation by insulin-degrading enzyme (IDE) was inhibited by ATP (Exp Biol Med 226:334-341, 2001). Then we studied ATP hydrolysis as a possible mechanism for reversion of this inhibition. ATP hydrolysis was determined by (32)P release after hydrolysis of gamma[(32)P]ATP. ATP hydrolysis was studied by Sephadex G200 chromatography, immunoprecipitation, and nondissociating gel electrophoresis. Purified recombinant rat IDE and extractive homogenous IDE showed similar ATP hydrolysis. All results showed concordance between insulin degradation and ATP hydrolysis, suggesting that IDE has both functions. In order to define the type of hydrolysis, we studied inhibitors of IDE, phosphohydrolases, and ATPases. Each substance studied had no effect on ATP hydrolysis, except 1 mM orthovanadate, a known inhibitor of ATPases, phosphatases, and insulin degradation. ATP hydrolysis followed a Michaelis-Menten kinetic with Vmax: 570.45 +/- 113.08 pmol Pi/hr and apparent Michaelis constant (Km): 63.13 +/- 3.48 microM. ATP binding studies strongly suggested an ATP binding site and enzyme kinetics established only one active hydrolytic ATP binding site per IDE molecule. ATP-induced enzyme aggregation changes as observed by electrophoresis mobility in nondissociating conditions and conformational changes on insulin binding as shown by IDE-insulin cross-linking. We conclude that IDEs have ATPase activity and that insulin-binding and degradation are dependent on ATP concentration; however, insulin does not modify the ATPase activity of IDE.