PMID:15205426
| Citation |
Buurman, ET, McLaggan, D, Naprstek, J and Epstein, W (2004) Multiple paths for nonphysiological transport of K+ in Escherichia coli. J. Bacteriol. 186:4238-45 |
|---|---|
| Abstract |
Mutants of Escherichia coli lacking all of the known saturable K+ transport systems, "triple mutants," require elevated K+ concentrations for growth. K+ transport activity in such mutants, called TrkF activity, has low substrate specificity and a low rate that increases with increasing external pH. Attempts to isolate mutants requiring even higher concentrations of K+ failed, implying that either TrkF is essential or is composed of multiple minor K+ transport activities. Instead, we sought mutations that allowed triple mutants to grow at lower K+ concentrations. Mutations so identified include ones altering MscL, the large mechanosensitive channel, or Opp, the oligopeptide permease. However, a possible contribution of wild-type Opp and MscL to TrkF activity was not proven. In contrast, expression of wild-type ProP, TrkG, and TrkH proteins increased uptake when encoded on multicopy plasmids. In all of these situations, the driving force for K+ appeared to be the transmembrane electric potential, and in most cases substrate specificity was low; these are characteristics of TrkF activity. These results support the view that TrkF is composed of multiple, "aberrant" K+ transport activities, i.e., paths that, regardless of their physiological function, allow K+ to cross the cell membrane by a uniport process. |
| Links |
PubMed PMC421619 Online version:10.1128/JB.186.13.4238-4245.2004 |
| Keywords |
Carrier Proteins/physiology; Escherichia coli/metabolism; Escherichia coli Proteins/physiology; Hydrogen-Ion Concentration; Ion Transport; Membrane Proteins/physiology; Potassium/metabolism; Receptor, trkA |
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