COMPARATIVE-STUDIES OF THE SPI1 PROTEINS OF 3 EQUINE ALPHA-1-PROTEINASE INHIBITOR HAPLOTYPES FOLLOWING ISOLATION BY AFFINITY-CHROMATOGRAPHY

1. Antiproteinase deficiency can result in excessive proteinase-induce d tissue damage. The major anti-elastase (Spil) protein of equine alph a1-proteinase inhibitor (alpha1-PI) was isolated from the plasma/serum of three common haplotypes (I, L and U). 2. The N-terminal amino acid sequences of the three inhibitors were identical, but were only appro x 65-77% homologous with two other published equine Spil sequences. 3. All three inhibitors complexed quickly and irreversibly with equine l eucocyte proteinase 2A (k(ass) = 2 x 10(7) m-1 sec-1). They were also efficient inhibitors of chymase (rat mast cell proteinase-II; k(ass) = 2 x 10(5) M-1 sec-1; K(i) = 2 x 10(-10) M). There was therefore no ev idence of deficient inhibition in the Spil variants of the I,L and U h aplotypes.