title: Valinomycin-induced cation transport in vesicles does not reflect the activity of K+ transport systems in Escherichia coli.
abstract: Transport systems for K+ in Escherichia coli are not detectable in membrane vesicles, but vesicles will take up K+ (and Rb+) in the presence of valinomycin. It is generally believed that valinomycin acts as a lipid-soluble cation carrier and that it does not interact with or activate cation transport systems. This view is challenged by Bhattacharyya et al. (Proc. Natl. Acad. Sci. USA 68:1448-1492, 1971), who reported reduced uptake in vesicles from E. coli mutants with K+ transport defects. We reexamined this question with some of the same mutants and were unable to confirm a correlation of valinomycin-induced vesicle transport with transport properties in intact cells. We found great variability in transport activity of vesicles from these E. coli K-12 strains and believe such variability as well as possible contamination with intact cells accounts for the earlier report. Our data do not support the idea that valinomycin-mediated transport in vesicles is related to physiological K+ transport systems.
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000166:cytology / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D014634:Valinomycin / Q000494:pharmacology*
chemical_list: D007476:Ionophores; D014634:Valinomycin; D012413:Rubidium; D011188:Potassium