The isoinhibitors of chymotrypsin/elastase from Ascaris lumbricoides: Isolation by affinity chromatography and association with the enzymes

Five isoinhibitors, proteins that inactivate chymotrypsin and elastase, were isolated from aqueous extracts of the intestinal parasite Ascaris lumbricoides var. suum by affinity chromatography. They were named in the order that they eluted from a CM-Sephadex C-25 column at pH 8.6 using a salt gradient. Isoinhibitor 1, first reported in this paper, is anionic on polyacrylamide gel electrophoresis at pH 9.3. The other four isoinhibitors are cationic on electrophoresis at pH 9.3, separable from each other, and identical with those reported previously [ R. J. Peanasky and G. M. Abu-Erreish (1971) in Proceedings International Research Conference on Proteinase Inhibitors (Fritz, H., and Tschesche, H., eds.), pp. 281–293, de Gruyter, New York]. Amino acid compositions show differences between the isoinhibitors. Antibody to isoinhibitor 1 reacts with its self-antigen only. Antibody to isoinhibitor 5 reacts with isoinhibitors 2–5 but not with isoinhibitor 1. Association equilibrium constants show that each of the isoinhibitors interacts most avidly with α-chymotrypsin. For isoinhibitor 1, the K a for α-chymotrypsin was 2.6 × 10 11 m −1, for porcine elastase 11.6 × 10 10 m −1, and for subtilisin Carlsberg 3.3 × 10 7 m −1. For isoinhibitors 2–5, the K a ranges were 7.1 × 10 10 to 1.3 × 10 10 m −1 for α-chymotrypsin, 1.0 × 10 9 to 5.6 × 10 9 m −1 for porcine elastase I, and 6.0 × 10 8 to 1.3 × 10 9 m −1 for subtilisin Carlsberg. Because of the strong affinity of these inhibitors for α-chymotrypsin and elastase, two proteins in the normal environment of the nematode, the name isoinhibitors of chymotrypsin/elastase is suggested for these proteins.