Interaction of neutrophil elastase with hydrophobic polyanionic chelators

The polyanionic calcium chelators, ethylenediamine-tetraacetic acid (EDTA), ethylene-bis-(oxyethylenenitrilo)-tetraacetic acid (EGTA), [bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA), 1-[2-amino-5-(6-carboxyindol-2-yl) phenoxyl]-2-(2'-amino-5'-methylphenoxy)ethane-N,N,N1, N1-tetraacetic acid (INDO-1), 1-[2-(5-carboxyoxazol-2yl)-6-phenoxyl]-2-(2'-amino-5'- methylphenoxy)ethane-N,N,N',N'-tetraacetic acid (FURA-2), and 2-([2-bis-(carboxymethyl)-amino-5-methylphenoxy]-methyl(-6-methyl-8- bis-(bis-(carboxymethyl)-aminoquinoline (QUIN-2), are all inhibitors of amidolytic activity of human neutrophil elastase (HNE). With MeOSuc-Ala-Ala-Pro-Val-pNA as substrate, these chelators all display mixed partial competitive and partial noncompetitive inhibition, but with the smaller substrate, pGlu-Pro-Val-pNA, only the noncompetitive component persists. The most effective inhibitor is FURA-2, with an apparent Ki of 0.5-0.7 mM. QUIN-2 is somewhat less effective, with a Ki of 2 mM, while EDTA is much less effective, with a Ki of 7 mM. In general, the more hydrophobic chelators are the best inhibitors, although INDO-1, which is about the same size as FURA-2, is surprisingly ineffective as an inhibitor. The chelators no longer function as effective inhibitors if their carboxyl groups are blocked by esterification with acetoxymethyl groups or by complexation with calcium ions, indicating that their binding to HNE is mediated in part through electrostatic interactions with a center of positive charge on the protein.(ABSTRACT TRUNCATED AT 250 WORDS)