The interaction between chymotrypsin and horse leucocyte neutral proteinases inhibitor

The inhibition of alpha-chymotrypsin by horse leucocyte neutral proteinases inhibitor was time-dependent with synthetic substrate N-benzoyl-L-tyrosine ethyl ester but not with azo-casein. This time dependence could be used to calculate the rate constant kass for the association of the inhibitor with bovine alpha-chymotrypsin (kass = 0.3 X 10(6)M-1 S-1). The inhibitor reacted with chymotrypsin at a molar a ratio of 1 : 1. The dissociation constant Ki = 0.30 X 10(9)M of the complex indicates a very strong interaction between enzyme and inhibitor.