RRC ID 4927
Author Kim JH, Lim BC, Yeom SJ, Kim YS, Kim HJ, Lee JK, Lee SH, Kim SW, Oh DK.
Title Differential selectivity of the Escherichia coli cell membrane shifts the equilibrium for the enzyme-catalyzed isomerization of galactose to tagatose.
Journal Appl Environ Microbiol
Abstract An Escherichia coli galactose kinase gene knockout (DeltagalK) strain, which contains the l-arabinose isomerase gene (araA) to isomerize d-galactose to d-tagatose, showed a high conversion yield of tagatose compared with the original galK strain because galactose was not metabolized by endogenous galactose kinase. In whole cells of the DeltagalK strain, the isomerase-catalyzed reaction exhibited an equilibrium shift toward tagatose, producing a tagatose fraction of 68% at 37 degrees C, whereas the purified l-arabinose isomerase gave a tagatose equilibrium fraction of 36%. These equilibrium fractions are close to those predicted from the measured equilibrium constants of the isomerization reaction catalyzed in whole cells and by the purified enzyme. The equilibrium shift in these cells resulted from the higher uptake and lower release rates for galactose, which is a common sugar substrate, than for tagatose, which is a rare sugar product. A DeltamglB mutant had decreased uptake rates for galactose and tagatose, indicating that a methylgalactoside transport system, MglABC, is the primary contributing transporter for the sugars. In the present study, whole-cell conversion using differential selectivity of the cell membrane was proposed as a method for shifting the equilibrium in sugar isomerization reactions.
Volume 74(8)
Pages 2307-13
Published 2008-4-1
DOI 10.1128/AEM.02691-07
PII AEM.02691-07
PMID 18263746
PMC PMC2293144
MeSH Aldose-Ketose Isomerases / isolation & purification Aldose-Ketose Isomerases / metabolism* Cell Membrane / metabolism* Escherichia coli / enzymology Escherichia coli / genetics Escherichia coli / growth & development Escherichia coli / metabolism* Escherichia coli Proteins / genetics Escherichia coli Proteins / metabolism* Galactokinase / genetics Galactose / metabolism* Gene Deletion Hexoses / metabolism* Kinetics
IF 4.077
Times Cited 6
Prokaryotes E. coli ME9062(BW25113) ME7986(MG1655)