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Journal of Bacteriology, December 2008, p. 7932-7938, Vol. 190, No. 24
0021-9193/08/$08.00+0     doi:10.1128/JB.01008-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Induction of the Galactose Enzymes in Escherichia coli Is Independent of the C-1-Hydroxyl Optical Configuration of the Inducer D-Galactose{triangledown}

Sang Jun Lee, Dale E. A. Lewis, and Sankar Adhya*

Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4264

Received 22 July 2008/ Accepted 3 October 2008

The two optical forms of aldohexose galactose differing at the C-1 position, {alpha}-D-galactose and β-D-galactose, are widespread in nature. The two anomers also occur in di- and polysaccharides, as well as in glycoconjugates. The anomeric form of D-galactose, when present in complex carbohydrates, e.g., cell wall, glycoproteins, and glycolipids, is specific. Their interconversion occurs as monomers and is effected by the enzyme mutarotase (aldose-1-epimerase). Mutarotase and other D-galactose-metabolizing enzymes are coded by genes that constitute an operon in Escherichia coli. The operon is repressed by the repressor GalR and induced by D-galactose. Since, depending on the carbon source during growth, the cell can make only one of the two anomers of D-galactose, the cell must also convert one anomer to the other for use in specific biosynthetic pathways. Thus, it is imperative that induction of the gal operon, specifically the mutarotase, be achievable by either anomer of D-galactose. Here we report in vivo and in vitro experiments showing that both {alpha}-D-galactose and β-D-galactose are capable of inducing transcription of the gal operon with equal efficiency and kinetics. Whereas all substitutions at the C-1 position in the {alpha} configuration inactivate the induction capacity of the sugar, the effect of substitutions in the β configuration varies depending upon the nature of the substitution; methyl and phenyl derivatives induce weakly, but the glucosyl derivative does not.

* Corresponding author. Mailing address: Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264. Phone: (301) 496-2495. Fax: (301) 480-7687. E-mail: sadhya{at}helix.nih.gov

{triangledown} Published ahead of print on 17 October 2008.

Journal of Bacteriology, December 2008, p. 7932-7938, Vol. 190, No. 24
0021-9193/08/$08.00+0     doi:10.1128/JB.01008-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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