Hofmeister effect on catalytic properties of chymotrypsin is substrate-dependent

Effect of Hofmeister sodium salts, sulfate, chloride, bromide and perchlorate, on catalytic properties and stability of chymotrypsin has been studied by absorbance and circular dichroism spectroscopies. To address Hofmeister effect on activity of chymotrypsin, two different substrates, N-benzoyl-L-tyrosine ethyl ester and amide N-succinyl-L-phenylalanine-p-nitroanilide, were used. Catalytic activity of chymotrypsin is dependent on salt concentration and position of anion in Hofmeister series. The enzyme activity for both substrates is only slightly affected by chaotropic anions and increases with kosmotropic nature of anions. While the trend of Hofmeister effect on chymotrypsin catalysis is similar for both substrates, the amplitude of the effect significantly differs. In the presence of 1 M sulfate, catalytic efficiency increased by ~2-fold for the ester but ~20-fold for the amide substrate. Positive correlation between stability and activity of chymotrypsin indicates the interdependence of these enzyme properties and is in agreement with recently developed macromolecular rate theory suggesting an important role of protein dynamics in enzyme catalysis. Linear dependencies of catalytic properties of chymotrypsin with partitioning of anions at bulk water/air as well as at hydrocarbon surface strongly indicate that the modulated enzyme properties are results of direct interaction of anions with protein surface.