N-Benzoyl-D-tyrosine

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.

The reverse micelle (RM) media are very good as nanoreactors because they can create a unique microenvironment for carrying out a variety of chemical and biochemical reactions. The aim of the present work is to determine the influence of different water-dimethyl sulfoxide (DMSO) mixtures encapsulated in 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/n-heptane RMs on the enzymatic hydrolysis of N-benzoyl-L-tyrosine p-nitroanilide (Bz-Try-pNA) by α-chymotrypsin (α-CT). The reaction was first studied in homogeneous media at different DMSO-water mixture compositions and in DMSO-water/AOT/n-heptane RMs. The hydrolysis rates of Bz-Try-pNA catalyzed by α-CT were determined by UV-vis spectroscopy. The reaction follows the Michaelis-Menten mechanism and the kinetic parameters: kcat, KM, and kcat/KM were evaluated under different conditions. In this homogeneous media, DMSO plays an important role in the solubilization process of the peptide which is almost insoluble in water, but it has a tremendous impact on the inactivation of α-CT. It is shown that the enzyme dissolved in a 20% molar ratio of the DMSO-water mixture does not present enzymatic activity. Dynamic light scattering has been used to assess the formation of DMSO-water/AOT/heptane RMs at different DMSO compositions. The results also show that there is preferential solvation of the AOT RM interface by water molecules. To test the use of these RMs as nanoreactors, the kinetic parameters for the enzymatic reaction in these systems have been evaluated. The parameters were determined at fixed W(S) {W(S) = ([water] + [DMSO])/[AOT] = 20} at different DMSO-water compositions. The results show that the Michaelis-Menten mechanism is valid for α-CT in all the RM systems studied and that the reaction takes place at the RM interface. Surprisingly, it was observed that the enzyme encapsulated by the RMs show catalytic effects with similar kcat/KM values at any DMSO composition investigated, which evidence that DMSO molecules are localized far from the RM interface.

Protease inhibitors of protein nature are rich in seeds of legume crops. There are two common types: Kunitz inhibitor, which mainly inhibits trypsin, and Bowman-Birk inhibitor, which inhibits both trypsin and chymotrypsin. Historically, trypsin inhibitor activity in legume products has been of primary interest for measurement. However, as plant proteins are increasingly used for food or feed in recent years, there is a growing interest in monitoring chymotrypsin inhibitor activity (CIA) in these products as well. Reported methods for CIA assay vary greatly and are incompletely described. No standardized or official method is available. The present study focused on developing a robust method for accurately measuring CIA, using N-benzoyl-L-tyrosine p-nitroanilide (BTpNA) as a substrate. Since BTpNA is not water soluble, a water-miscible organic solvent must be present. After investigating the effects of several factors, such as absorption spectra, organic solvent type and concentration, substrate and enzyme concentrations, inhibitor levels (which affected % chymotrypsin inhibition), the sequence of adding reagents, extractant and extraction time, and so forth, an optimized method for CIA measurement was finally developed. It features dimethylformamide as the organic solvent, the enzyme-last sequence, 5 ml total assay volume, and calculation of the inhibitor activity based on 40% chymotrypsin inhibition. The method can also be slightly modified for measuring chymotrypsin activity. The robust performance of the method was verified by measuring 11 assorted protein products, paving a way for standardization. PRACTICAL APPLICATION: With an increasing use of plant proteins, there is an urgent need to measure chymotrypsin inhibitor activity in various protein products with accuracy. After thoroughly investigating several factors, an optimized method for measuring chymotrypsin inhibitor activity in various protein products was developed. The proposed method is sensitive and robust, providing a basis for standardization. It can also be used for measuring chymotrypsin activity.