Isolation, chemical, and physical properties of α-1-antitrypsin

Abstract

Interest in .alpha.-1-antitrypsin has been stimulated by studies which suggest a possible role in human diseases. A method of isolation of .alpha.-1-antitrypsin (.alpha.-1-AT) in good yield from normal human plasma is described. A key step was affinity chromatography employing an antiserum which had been depleted of .alpha.-1-AT antibodies. The final preparations were homogeneous by immunological and physicochemical criteria. The specific activity of the purified .alpha.-1-AT was 0.363 mg of active bovine trypsin inhibited per 1.0 mg of inhibitor. Polyacrylamide gel patterns at both alkaline and acid pH of highly pure preparations frequently, but not invariably, showed multiple bands. Molecular weight studies by sedimentation equilibrium ultracentrifugation in aqueous buffer and in 6 M guanidine and sodium dodecyl sulfate polyacrylamide gel electrophoresis suggest that .alpha.-1-AT is a single polypeptide chain having a molecular weight of 49,500. Other physical and chemical properties of the inhibitor are described. A limited N-terminal sequence (Glu-Asp-Pro-Gln-Gly-Asx-Ala-Ala) was obtained. .alpha.-1-AT easily forms polymers and higher aggregates when exposed to denaturing agents such as 8 M urea and 6 M guanidine. Aggregation may be determined by both covalent and noncovalent forces.