Characterization of Sheep Alpha-1-Proteinase Inhibitor: Important Differences from the Human Protein

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Abstract
The plasma proteinase inhibitor corresponding to alpha-1-proteinase inhibitor (.alpha.1PI) in humans was isolated from sheep plasma. Ovine .alpha.1PI is of higher molecular weight (62,000 daltons) than is human .alpha.1PI, is resistant to chemical oxidation by N-chlorosuccinimide, and has poor elastase-inactivating power compared with the corresponding inhibitor in humans. However, ovine .alpha.1PI is a potent trypsin inhibitor. Despite the differences indicated above, a partial homology (22 to 35) exists between human and sheep .alpha.1PI, at least as analyzed through the first 20 residues of the sheep inhibitor. The weak elastase-inhibitory capacity of sheep .alpha.1PI is paralleled by the low content of elastase in the sheep neutrophil granule. These important difference between sheep and human neutrophils and plasma proteinase inhibitors should be borne in mind in designing experiments related to proteolytically mediated lung injury in the former species.