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Thermodynamic parameters monitoring the equilibrium shift of enzyme‐catalyzed hydrolysis/synthesis reactions in favor of synthesis in mixtures of water and organic solvent
Author(s) -
Deschrevel Brigitte,
Vincent JeanClaude,
Ripoll Camille,
Thellier Michel
Publication year - 2002
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.10458
Subject(s) - chemistry , equilibrium constant , hydrolysis , catalysis , solvent , dipeptide , chemical equilibrium , thermodynamic equilibrium , reaction rate , water activity , organic chemistry , reaction rate constant , hydrolysis constant , inorganic chemistry , kinetics , thermodynamics , amino acid , water content , biochemistry , physics , geotechnical engineering , quantum mechanics , engineering
The main strategy developed to shift the equilibrium state of a hydrolase‐catalyzed hydrolysis/synthesis reaction consists in reducing water activity by addition of organic solvents in the reaction medium. We have used several mixtures of water and 1,4‐butanediol, ranging from pure water to pure 1,4‐butanediol, to study the hydrolysis/synthesis reaction of the N ‐Cbz‐ L ‐tryptophanyl‐glycineamide dipeptide, catalyzed by α‐chymotrypsin. In the presence of 1,4‐butanediol, α‐chymotrypsin also catalyzed the esterification reaction between this diol and N ‐Cbz‐ L ‐tryptophan; this ester hydrolysis/synthesis reaction has thus also been examined. The dipeptide and ester equilibrium concentrations increase when the water content of the reaction medium is decreased. Using our experimental data, we have determined the equilibrium constants of the hydrolysis/synthesis equilibria involving the nonionized forms of the protected amino acids, the estimated values of which are Ksp = 8 10 5 for the dipeptide and Kse = 78 for the ester respectively. They are true thermodynamic equilibrium constants, each related to a single, well‐defined reaction equilibrium and with water activity being taken into account. If an organic solvent is added to the reaction medium these equilibria can be shifted towards synthesis by decreasing the water activity but also by modifying the ionization/neutralization equilibrium constant of the ionizable groups. These two effects depend both on the water content and on the nature of the organic solvent used, and, in particular, on its dielectric constant. Because of the importance of this parameter in our study, we discuss using it as an indicator to select an appropriate organic solvent to perform an enzyme‐catalyzed synthesis. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 81: 167–177, 2003.