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Influence of ionic liquid cosolvent on transgalactosylation reactions catalyzed by thermostable β‐glycosylhydrolase CelB from Pyrococcus Furiosus
Author(s) -
Lang Markus,
Kamrat Thomas,
Nidetzky Bernd
Publication year - 2006
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.21068
Subject(s) - chemistry , pyrococcus furiosus , ionic liquid , yield (engineering) , lactose , hydrolysis , catalysis , xylose , chromatography , organic chemistry , biochemistry , materials science , fermentation , metallurgy , archaea , gene
The synthesis of glycosides by enzymatic transglycosylation is a kinetically controlled reaction performed in the context of a non‐favorable thermodynamic equilibrium. An unreactive organic cosolvent which increases the selectivity of the enzyme for glycosyl transfer to the acceptor nucleophile compared with water ( K sel ) could improve maximum product yield. Here we report on the effect of the ionic liquid 1,3‐dimethylimidazoliummethylsulfate on hydrolase and transferase activities of the hyperthermostable β‐glycosidase CelB from the archaeon Pyrococcus furiosus . CelB retained full catalytic efficiency for lactose hydrolysis at 80°C in a 50% (by vol.) solution of ionic liquid in sodium citrate buffer, pH 5.5. It was inactive but not irreversibly denatured at 70% ionic liquid. Using lactose (0.15 M) as galactosyl donor, values of K sel for a representative series of eight acceptor alcohols were determined in kinetic assays at 80°C and found to increase between 1.3‐fold ( D ‐xylose) and 3.1‐fold (glycerol) in 45% ionic liquid. Enhancement of K sel was dependent on ionic liquid concentration and higher than expected from the decrease in water activity caused by the cosolvent. Experimental molar ratios of D ‐glucose and D ‐galactose produced during enzymatic conversion of lactose (75–150 mM) in the presence of D ‐xylose (0.5 M) or glycerol (0.5 M) showed excellent agreement with predictions based on K sel values and confirm a significant, yet moderate effect of 45% ionic liquid on increasing the yield of D ‐galactoside product, by ≤10%. © 2006 Wiley Periodicals, Inc.