The temperature dependence of steady-state kinetics: what can be learned about pig liver esterase stereospecificity?
The steady-state kinetic parameters for pig liver carboxylesterase (PLE)-catalyzed hydrolysis of the prochiral substrate dimethyl phenylmalonate (DMPM) (product enantioselectivity) and the separate enantiomers of three chiral 2-phenylpropionic acid esters (substrate enantioselectivity) were measured at seven temperatures between 288 K and 312 K. Arrhenius plots of turnover numbers against the reciprocal of experimental temperatures yielded enthalpies and entropies of activation at enzyme saturation. (+)-(S)-methyl-2-phenylpropionate, (+)-(S)-4-nitrophenyl 2-phenylpropionate, and both enantiomers of phenyl 2-phenylpropionate showed very similar activation enthalpies and entropies (approximately 50 kJ mol-1 and -50 J mol-1 K-1, respectively), but differences were observed for (-)-(R)-methyl 2-phenylpropionate and (-)-(R)-4-nitrophenyl 2-phenylpropionate. Whereas the entropies of activation of all 2-phenylpropionates were negative, positive entropies of activation were measured in the formation of monomethyl phenylmalonate enantiomers from DMPM. Enthalpy-entropy compensation analysis of the data indicates a common mechanism of PLE substrate and product enantiospecificity in the reactions studied here.
School of Pharmacy, University of Lausanne, Switzerland.
H
H
Van Gelderen
J M
JM
Mayer
S
S
Cellamare
B
B
Testa
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004950:Esterases / Q000737:chemistry / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D011422:Propionates / Q000378:metabolism; D051381:Rats; D013237:Stereoisomerism; D013552:Swine; D013696:Temperature; D013816:Thermodynamics
D011422:Propionates; D004950:Esterases