The primary elastase inhibitor (elastasin) and trypsin inhibitor (contrapsin) in the goat are serpins related to human alpha 1-anti-chymotrypsin.

Two primary serine proteinase inhibitors in goat plasma have been isolated and characterized. The N-terminal sequence analysis of the purified proteins revealed that they are closely related to each other and are highly homologous to human alpha 1-anti-chymotrypsin rather than alpha 1-proteinase inhibitor. However, despite structural similarities the inhibitory specificity of the goat inhibitors differed from each other and from that of anti-chymotrypsin. In contrast with human anti-chymotrypsin, one of the goat inhibitors was shown to be a strong and specific inhibitor of trypsin (k(ass.) = 1.9 x 10(6) M-1.s-1), whereas the other was an efficient inhibitor of neutrophil elastase (k(ass.) = 1.5 x 10(6) M-1.S-1). Differences in the inhibitory specificity of each protein could readily be attributed to the amino acid sequence within the reactive site region. The trypsin inhibitor with an assumed arginine residue at the P1 position of the reactive-site peptide bond is referred to as 'contrapsin', and indicates that the occurrence of contrapsins is not restricted to rodents. In contrast, the inhibitory specificity, resistance to oxidative and proteolytic inactivation and the presence of a P1 leucine residue in the elastase inhibitor is unique among inhibitory serpins that have been characterized to date. Because this serpin is apparently the major elastase inhibitor in goat plasma, it is likely to be involved in the control of goat neutrophil elastase. Therefore, we suggest the name 'elastasin', and extend it to any other anti-chymotrypsin related serpins possessing neutrophil-elastase- inhibitory activity.