Purification and characterization of an α2-macroglobulin-like proteinase inhibitor from plasma of the crayfish Pacifastacus leniusculus

Abstract

An α2-macroglobulin (α2M)-like proteinase inhibitor from plasma of the crayfish Pacifastacus leniusculus was purified to apparent homogeneity by acid precipitation, hydrophobic interaction chromatography, affinity chromatography on concanavalin A-Sepharose and anion-exchange chromatography. The subunit M(r) is about 190000. Pore-size-limit electrophoresis proved the native protein to be a dimer. The purified protein resembled vertebrate α2Ms in that it protected trypsin from inhibition by soyabean trypsin inhibitor, and in its sensitivity to methylamine treatment. Methylamine also prevented the protein from being autolytically cleaved into M(r) 60000 and 140000 fragments when subjected to heat treatment. The amino acid composition showed similarities with both human α2M and an α2M-like protein from the arthropod Limulus polyphemus. These data indicate that this Pacifastacus α2M-like protein (Pα2M) may be a distantly related homologue of vertebrate α2Ms.