Determination of elastase inhibitory activity of α₁-proteinase inhibitor and bronchial antileukoprotease: Different results using insoluble elastin or synthetic low molecular weight substrates

Abstract

We have determined the effect of two elastase-specific synthetic low molecular weight substrates, L-pyroglutamylprolylvaline-paranitroanilide and succinyl-trialanylparanitroanilide, together with insoluble elastin-fluorescein, on the determination of the neutrophil elastase (NE) inhibitory capacity of purified α₁-proteinase inhibitor (α₁-PI) and bronchial antileukoprotease (ALP). In addition, the inhibitory capacities of mixtures of α₁-proteinase inhibitor, antileukoprotease and α₂-macroglobulin prepared in ratios similar to that in lung secretions were determined. Purified inhibitors, alone or in combinations, inhibited about 1 mole neutrophil elastase per mole inhibitor when assessed using synthetic substrates. However, when elastin-fluorescein was used in the assay system, the purified inhibitors showed an inhibitory capacity that was 40–85% of the value obtained using synthetic substrates. Even less inhibition was observed when mixtures of inhibitors were assessed using elastin-fluorescein (23–44% of the value for synthetic substrates). Our data indicate that results of elastase inhibitor activity measurements depend on the type of substrate which has been used.

Key words:

• antileukoprotease
• elastase
• elastin
• α₁-proteinase inhibitor
• proteinase inhibitors
• synthetic substrates