Counterflow efflux of thiamin in Escherichia coli

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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 2 · 10−2M 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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