Counterflow efflux of thiamin in Escherichia coli |
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Authors: | Takahiro Nishimune Masaaki Tomita Zensaku Yoshii Ryoji Hayashi |
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Affiliation: | 1. Department of Microbiology, Yamaguchi University School of Medicine, Ube, Yamaguchi-ken Japan;2. Medical College of Oita, Oita-ken Japan |
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Abstract: | A resting cell of Escherichia coli lacking thiamin kinase incorporated external thiamin with an energy-dependent counterflow efflux (C-efflux). This C-efflux could be separated from an energy-dependent exit by a selective inhibition of exit by NaN3. The extracellular thiamin could be replaced by thiamin diphosphate, resulting in the same rate of C-efflux, but the rate of C-efflux of intracellular thiamin diphosphate against the external thiamin was markedly low. This low rate of C-efflux of thiamin diphosphate could explain the higher accumulation of the compound than that of free thiamin in the thiamin-kinase-defective mutant as well as in its wild-type parent. Basic characteristics of free thiamin uptake and exit in E. coli W mutant were compared with those reported in K 12 mutant: a marked difference existed in the rate of exit. The low rate of exit in E. coli W 70-23-102 was inferred as the reason for the absence of an overshoot phenomenon of thiamin uptake in this strain. |
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Keywords: | Thiamin uptake Counterflow efflux Thiamin kinase E. coli mutant FCCP, trifluoromethoxy carbonylcyanide phenylhydrazone DCCD, dicyclohexylcarbodiimide |
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