[Intraglobular electrostatic field of an enzyme. IV. Electrolytic dissociation of the active center of alpha-chymotrypsin].

The dissociation of the ionogenic groups of the active centre of alpha-chymotrypsin is considered taking into account effects of short- and long-range solvation and intraglobular electric field. The ionic pair Asp102-CO2-. His57-ImH+ is shown to be the most probable state of the neutral active centre of alpha-chymotrypsin, this ionic pair being stabilized substantially through electrostatic interaction of the ions. The pair dissociates releasing the proton from the N epsilon 2 atom of His57 and forming a catalytically active group Asp102-CO2-. His57-Im. The pK value approximately 7 characteristic of this acid-base equilibrium pertains to the active centre as a whole rather than to the isolated imidazolium ion. The approach developed by the authors is compared with other works in this area.