Nature of the Inactivation of Elastase by N-Peptidyl-O-aroyl hydroxylamine as a Function of pH

Abstract

The mechanism of inactivation of porcine pancreatic elastase (PPE) by N-peptidyl-Oaroylhydroxylamine was studied by X-ray crystallography. The inactivator forms a stable complex with the enzyme by means of a covalent attachment to the active site Ser 203(195) Oγ. The nature of the complex is, however, different depending on the pH at which the inactivation reaction occurs. At pH 5, the complex formed is a hydroxylamine derivative of Ser 203(195) in which the Oγ of serine is the oxygen of the hydroxylamine derivative. At pH 7.5, the complex formed is a carbamate derivative at Ser 203(195)Oγ. In both types of complexes, the inactivator binds in the S' subsites of the enzyme instead of forming the usual antiparallel β-sheet with the S subsites. The implication for the mechanism of inactivation at different pHs is discussed. © 1995, American Chemical Society. All rights reserved.