Horse alpha-1 protease inhibitors: relationship between the slow (S) and fast (F) isoforms

Horse alpha-1 protease isoinhibitors were isolated in a highly purified form using individually designed fractionation procedures. The isoinhibitors, running in agarose gel electrophoresis at pH 8.6 as two distinct bands, were designated S alpha-1 and F alpha-1. The molecular relationships between S alpha-1 and F alpha-1 were investigated by using classical electrophoretic and immunoelectrophoretic methods. No differences between the inhibitors were revealed with respect to their antiproteolytic activity, determined by fibrinogen agarose gel electrophoresis assays. No immunological differences between the isoforms were detected. These observations, together with others reported in this paper, suggest that the two isoinhibitors are probably the monomeric and dimeric form of the same molecule.