Open AccessEnhanced Asymmetric Reduction of Ethyl 3‐Oxobutyrate by Baker's Yeast via Substrate Feeding and Enzyme Inhibition
Author(s) -
Fow K.L.,
Poon L. C. H.,
Sim S. T.,
Chuah G. K.,
Jaenicke S.
Publication year - 2008
Publication title -
engineering in life sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.547
H-Index - 57
eISSN - 1618-2863
pISSN - 1618-0240
DOI - 10.1002/elsc.200700052
Subject(s) - yeast , substrate (aquarium) , chemistry , enzyme , enantiomeric excess , biocatalysis , ethyl acetate , fermentation , stereochemistry , biochemistry , enantioselective synthesis , catalysis , biology , reaction mechanism , ecology
The moderate enantioselectivity of wild form baker's yeast can be considerably increased either by using continuous feeding to maintain a low substrate concentration throughout the reaction, or by the selective inhibition of competing enzymatic pathways. The reduction of ethyl 3‐oxobutyrate to ethyl ( S )‐3‐hydroxybutyrate was used as a model reaction. With the substrate feeding method, the enantioselectivity could be increased from 75 % to as high as 98 %. The increased selectivity originates from the much higher substrate binding constant of the ( R )‐specific enzymes, so that these enzymes remain essentially inactive if a low concentration of ethyl 3‐oxobutyrate is maintained in the bioreactor. Alternatively, the enantioselectivity of baker's yeast can be improved by selectively blocking competing enzymatic pathways. It was found that vinyl acetate is a selective inhibitor for the ( R )‐specific enzymes. Ethyl ( S )‐3‐hydroxybutyrate with an enantiomeric excess of 98 % was obtained by pre‐incubation of baker's yeast in 100 mM of vinyl acetate solution for 1 h. These results suggest that by selecting appropriate process conditions, natural baker's yeast can be a competitive biocatalyst for the large‐scale production of chiral secondary alcohols.