Comparative studies of the Spi1 proteins of three equine alpha-1-proteinase inhibitor haplotypes following isolation by affinity chromatography.

1. Antiproteinase deficiency can result in excessive proteinase-induced tissue damage. The major anti-elastase (Spi1) protein of equine alpha 1-proteinase inhibitor (alpha 1-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 approx 65-77% homologous with two other published equine Spi1 sequences. 3. All three inhibitors complexed quickly and irreversibly with equine leucocyte proteinase 2A (kass = 2 x 10(7) M-1 sec-1). They were also efficient inhibitors of chymase (rat mast cell proteinase-II; kass = 2 x 10(5) M-1 sec-1; Ki = 2 x 10(-10) M). There was therefore no evidence of deficient inhibition in the Spi1 variants of the I,L and U haplotypes.