Isolation and characterization of two alpha1-protease inhibitors in rat serum

Two alpha1-protease inhibitors were identified in rat serum. On polyacrylamide gels, one (R-I) appeared at the leading edge of the albumin, the other (R-2) at the trailing edge. The two inhibitors have differing molecular weights, differing inhibitory spectra toward proteases, and are immunologically distinct. The assays for antiprotease activity were performed on whole human and rat sera and inhibitor-enriched fractions of rat serum that had been electrophoresed on polyacrylamide gels. The more rapidly migrating antiprotease of rat serum, R-I, inhibited trypsin, chymotrypsin, and elastase. The more slowly migrating antiprotease, R-2, inhibited both trypsin and chymotrypsin but possessed only weak anti-elastase activity. When a comparison was made between human alpha1-antitrypsin and the more rapidly migrating rat inhibitor, it could be seen that they have similar molecular weights, similar inhibitory spectra, and similar electrophoretic mobilities. The relevance of the study of the R-I inhibitor in the pathogenesis of experimental emphysema is emphasized.