Human pre-alpha-inhibitor: isolation from a by-product of industrial scale plasma fractionation and structural analysis of its H3 heavy chain
Abstract
Pre-alpha-inhibitor (P alpha I) is a serine proteinase inhibitor from human plasma. It comprises bikunin (BK) responsible for antiprotease activity, covalently linked to a heavy chain H3. Here we describe its isolation from a side fraction of an industrial preparation of plasma clotting factors. By using a highly specific polyclonal antiserum prepared from rabbit immunized with a H3P polypeptide obtained in a bacterial expression system, we were able to identify the fractions containing P alpha I. Then, taking advantage of the differential affinity of the members of the inter-alpha-inhibitor family (I alpha I) for heparin-Sepharose and blue-Sepharose, we isolated P alpha I. Its specific antitryptic activity was 580 IU/g, higher than that of I alpha I: 420 IU/g. Its M(r), determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, with or without prior reduction, was 130,000. Its peptide chains were identified by N-terminal sequencing. The H3 heavy chain was isolated from P alpha I by alkaline dissociation and anion-exchange chromatography. Its electrophoretic mobility was compared to that of the HI and H2 heavy chains of I alpha I. In reducing conditions, it was quite similar to that of H2 (M(r) 85,000) but clearly...Continue Reading
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