Characterization of Fumarate Transport in Helicobacter pylori |
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Authors: | GL Mendz DJ Meek SL Hazell |
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Institution: | (1) School of Biochemistry and Molecular Genetics, University of New South Wales, Sydney, 2052, Australia, AU;(2) School of Microbiology and Immunology, University of New South Wales, Sydney, 2052, Australia, AU |
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Abstract: | The fumarate transport system of the bacterium Helicobacter pylori was investigated employing radioactive tracer analysis. The transport of fumarate at micromolar concentrations was saturable
with a K
M
of 220 ± 21 μm and V
max of 54 ± 2 nmole/min/mg protein at 20°C, depended on temperature between 4 and 40°C, and was susceptible to inhibitors, suggesting
the presence of one or more fumarate carriers. The release of fumarate from cells was also saturable with a K
M
of 464 ± 71 μm and V
max of 22 ± 2 nmol/min/mg protein at 20°C. The rates of fumarate influx at millomolar concentrations increased linearly with
permeant concentration, and depended on the age of the cells. The transport system was specific for dicarboxylic acids suggesting
that fumarate is taken up via dicarboxylate transporters. Succinate and fumarate appeared to form an antiport system. The
properties of fumarate transport were elucidated by investigating the effects of amino acids, monovalent cations, pH and potential
inhibitors. The results provided evidence that influx and efflux of fumarate at low concentrations from H. pylori cells was a carrier-mediated secondary transport with the driving force supplied by the chemical gradient of the anion. The
anaerobic C4-dicarboxylate transport protein identified in the genome of the bacterium appeared to be a good candidate for the fumarate
transporter.
Received: 11 December 1997/Revised: 7 May 1998 |
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Keywords: | : Fumarate — Dicarboxylic acid — Transport — Radiotracer analyses — Helicobacter pylori |
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