Pressure effects on substrate activation phenomena in the alpha-chymotrypsin-catalyzed hydrolysis of p-nitrophenyl acetate.
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.
Makimoto
S
S
Department of Chemistry, Faculty of Science and Engineering Ritsumeikan University, Kyoto, Japan.
Taniguchi
Y
Y
D001274:Atmospheric Pressure; D002384:Catalysis; D002733:Chlorophenols / Q000378:metabolism; D002918:Chymotrypsin / Q000378:metabolism*; D004789:Enzyme Activation; D007700:Kinetics; D009596:Nitrophenols / Q000378:metabolism*; D011487:Protein Conformation
D002733:Chlorophenols; D009596:Nitrophenols; C029107:4-chlorophenol; C008642:4-nitrophenyl acetate; D002918:Chymotrypsin