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Applied and Environmental Microbiology, March 2000, p. 995-1000, Vol. 66, No. 3
Department of Animal Sciences, University of
Kentucky, Lexington, Kentucky 40546-0215
Received 30 August 1999/Accepted 12 December 1999
Thermoanaerobacter ethanolicus is a gram-positive
thermophile that produces considerable amounts of ethanol from
soluble sugars and polymeric substrates, including starch. Growth on
maltose, a product of starch hydrolysis, was associated with the
production of a prominent membrane-associated protein that had an
apparent molecular weight of 43,800 and was not detected in cells grown on xylose or glucose. Filter-binding assays revealed that cell membranes bound maltose with high affinity. Metabolic labeling of
T. ethanolicus maltose-grown cells with
[14C]palmitic acid showed that this protein was
posttranslationally acylated. A maltose-binding protein was
purified by using an amylose resin affinity column, and the binding
constant was 270 nM. Since maltase activity was found only in the
cytosol of fractionated cells and unlabeled glucose did not compete
with radiolabeled maltose for uptake in whole cells, it appeared that
maltose was transported intact. In whole-cell transport assays, the
affinity for maltose was approximately 40 nM. Maltotriose and
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Copyright © 2000, American Society for Microbiology. All rights reserved.
High-Affinity Maltose Binding and Transport by the Thermophilic
Anaerobe Thermoanaerobacter ethanolicus 39E
-trehalose competitively inhibited maltose uptake in transport
assays, whereas glucose, cellobiose, and a range of disaccharides
had little effect. Based on these results, it appears that T. ethanolicus possesses a high-affinity, ABC type transport system
that is specific for maltose, maltotriose, and
-trehalose.
*
Corresponding author. Mailing address: 212 W. P. Garrigus Building, Department of Animal Sciences, University of
Kentucky, Lexington, KY 40546-0215. Phone: (606) 257-7554. Fax:
(606) 257-5318. E-mail: strobel{at}pop.uky.edu.
Published with the approval of the Director of the Kentucky
Agricultural Experiment Station as Journal article no. 00-07-7.
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