Pressure effects on substrate activation phenomena in the alpha-chymotrypsin-catalyzed hydrolysis of p-nitrophenyl acetate |
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Authors: | S Makimoto Y Taniguchi |
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Affiliation: | Department of Chemistry, Faculty of Science and Engineering Ritsumeikan University, Kyoto, Japan. |
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Abstract: | With and without p-chlorophenol as an activator, the rates of hydrolysis of p-nitrophenyl acetate catalyzed by alpha-chymotrypsin were measured at pressures up to 2 kbar at 25 degrees C. From the pressure dependence of the rate constant (kcat)A and (kcat)0 of the product formation with and without an activator, the activation volumes (delta V not equal to cat)A and (delta not equal to cat)0 were +2 and -6 +/- 1 cm3.mol-1. From the pressure dependence of the equilibrium constant (KA) of incorporation of p-chlorophenol into the enzyme, the volume change (delta VA) was -10 +/- 1 cm3.mol-1. The mechanisms of the substrate activation are discussed in terms of the activation and reaction volumes. |
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