PMID:18263746

Citation	Kim, JH, Lim, BC, Yeom, SJ, Kim, YS, Kim, HJ, Lee, JK, Lee, SH, Kim, SW and Oh, DK (2008) Differential selectivity of the Escherichia coli cell membrane shifts the equilibrium for the enzyme-catalyzed isomerization of galactose to tagatose. Appl. Environ. Microbiol. 74:2307-13
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.
Links	PubMed PMC2293144 Online version:10.1128/AEM.02691-07
Keywords	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
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
ECOLI:GAL7		GO:0004335: galactokinase activity	ECO:0000315:		F		Figure 2	complete CACAO 5773
ECOLI:GAL7	enables	GO:0004335: galactokinase activity	ECO:0000315: mutant phenotype evidence used in manual assertion		F		Seeded From UniProt	complete

References

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