Purification and characterization of α₁-proteinase inhibitor and antithrombin III: major serpins of rainbow trout (Oncorhynchuss mykiss) and carp (Cyprinus carpio) blood plasma

Abstract

The main serine proteinase inhibitors of rainbow trout (Oncorhynchuss mykiss) and common carp (Cyprinus carpio) blood plasma were isolated and purified. The investigated inhibitors, α₁-proteinase inhibitor (α₁-PI) and antithrombin III (AT III), act by forming stable complexes with target proteinases. The association rate constants k _on for the interaction of fish plasma inhibitors with several serine proteinases have been determined: k _on for both carp and rainbow trout α₁-PI were >10⁷ M⁻¹ s⁻¹ for human neutrophil elastase, and in the case of bovine trypsin and chymotrypsin k _on values were 2.0–5.2 × 10⁶ M⁻¹ s⁻¹. Association rate constants k _on for the interaction of carp and rainbow trout AT III with bovine trypsin and thrombin were about 1.3 × 10⁴–7.9 × 10⁵ M⁻¹ s⁻¹ without and >10⁷ M⁻¹ s⁻¹ in presence of heparin; so antithrombins require the presence of heparin to become effective proteinase inhibitors. The high degree of homology of the estimated amino acid sequences of fish inhibitors reactive site loops confirms their similarity with other proteinase inhibitors from the serpin family.