A chymotrypsin inhibitor from the parastitic nematode, Oesophagostomum radiatum.

An inhibitor of alpha-chymotrypsin was isolated from O. radiatum by affinity chromatography, as well as by ion-exchange and molecular sieve chromatography. The inhibitor was associated with the cuticle or musculature of the parasite. It completely inhibited the esterolytic activity of chymotrypsin. Molecular sieve chromatography gave an apparent molecular weight of 9700 for the inhibitor alone and 32000 for the complex with chymotrypsin. This suggests reaction in a 1:1 molar ratio. The inhibitor reacted with diisopropyl phosphoryl-chymotrypsin weakly, if at all. Measurement of the dissociation constants for the enzyme-inhibitor complexes gave values of 2.2x10(-9) M for the product of affinity chromatography but less than 2x10(-10) M for all other preparations. Possible explanations of this are discussed.