Abstract
When the competitive inhibitor benzeneboronic acid (BBA) forms a complex with alpha-chymotrypsin [EC 3.4.21.1] protons are released in the acidic pH region. The proton release can be measured by a difference potentiometric technique. The proton release is also observed in chymotrypsinogen A but not in TRCK-, DIP-, and anhydrochymotrypsins. Based on these observations, a simple procedure to estimate the equilibrium constants of the trigonal-tetrahedral interconversion of BBA is proposed. Thermodynamic parameters of the ionization of His 57 and of each step involved in BBA binding can be estimated from the temperature dependence of the proton release. Those of His 57 are essentially the same as those of imidazole in water. Regarding the interconversion of BBA on the enzyme, the value of delta S is similar to delta S not equal to of the deacylation step of nonspecific substrates, and delta H is remarkably reduced from that for the ionization of BBA in water. The enthalpic gain of enzymic process is suggested to be due to the change of the proton acceptor, which is water in the case of the ionization of BBA in water, to imidazole on the enzyme.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.