Primary structure of a porcine leukocyte serpin.

Inhibitors of neutral serine proteinases (serpins) have been shown to be colocalized with their target enzymes in leukocytes of several mammalian species. Here we report the purification and complete primary structure of a cytosolic inhibitor from porcine granulocytes which is directed against neutrophil elastase. Two molecular mass forms of the leukocyte neutral proteinase inhibitor (LNPI) were isolated by affinity and ion-exchange chromatography followed by gel filtration, and identified as the inhibitorily active monomer and homodimer of the inhibitor protein. According to the amino acid sequence the molecular mass of the non-glycosylated inhibitor was calculated to 42,597 Da (378 amino acid residues). A sequence identity of 81% was found between LNPI and the homologous elastase inhibitors from both human and equine leukocytes, whereas only 50% of the positions are identical in LNPI and human plasminogen activator inhibitor 2. These data suggest that LNPI is a member of a new group of cytosolic serpins closely related to the ovalbumin branch of the superfamily.