Pre-alpha 2-elastase inhibitor of the horse: a hybrid molecule between alpha 1-proteinase inhibitor and alpha 2-beta 1-glycoprotein.

Pre-alpha 2-elastase inhibitor of horse plasma has recently been isolated in our laboratory. In this article we demonstrate that the inhibitor is a composite structure built of alpha 1-proteinase inhibitor and alpha 1-beta 1-glycoprotein. The compound inhibitor is biologically active, although it has previously been shown that its enzyme specificity is different from that of free alpha 1-proteinase inhibitor. Our observations are based on immunochemical cross-reactions between pre-alpha 1-elastase inhibitor and antibodies to alpha 2-beta 1-glycoprotein as well as antibodies to alpha 1-proteinase inhibitor. Pre-alpha 2-elastase inhibitor could be dissociated into its parent components by dithiothreitol. After dissociation, the alpha 1-proteinase inhibitor portion retained its biological activity.