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J. Bacteriol., Feb 1997, 1298-1306, Vol 179, No. 4
D Meyer, C Schneider-Fresenius, R Horlacher, R Peist and W Boos
glk, the structural gene for glucokinase of Escherichia coli, was cloned
and sequenced. Overexpression of glk resulted in the synthesis of a
cytoplasmic protein with a molecular weight of 35,000. The enzyme was
purified, and its kinetic parameters were determined. Its Km values for
glucose and ATP were 0.78 and 3.76 mM, respectively. Its Vmax was 158 U/mg
of protein. A chromosomal glk-lacZ fusion was constructed and used to
monitor glk expression. Under all conditions tested, only growth on glucose
reduced the expression of glk by about 50%. A fruR mutation slightly
increased the expression of glk-lacZ, whereas the overexpression of
plasmid-encoded fruR+ weakly decreased expression. A FruR consensus binding
motif was found 123 bp upstream of the potential transcriptional start site
of glk. Overexpression of glk interfered with the expression of the maltose
system. Repression was strongest in strains that exhibited constitutive mal
gene expression due to endogenous induction and, in the absence of a
functional MalK protein, the ATP-hydrolyzing subunit of the maltose
transport system. It was least effective in wild-type strains growing on
maltose or in strains constitutive for the maltose system due to a mutation
in malT rendering the mal gene expression independent of inducer. This
demonstrates that free internal glucose plays an essential role in the
formation of the endogenous inducer of the maltose system.
Copyright © 1997, American Society for Microbiology
Molecular characterization of glucokinase from Escherichia coli K-12
Department of Biology, University of Konstanz, Germany.
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