The respiration-driven active sodium transport system in E. coli does not function with lithium.
Comparison of respiration-driven active transport of alkali cations from E. coli cells loaded with Na+ or Li+ showed that Li+ could not be expelled from the cells like Na+. K+ accumulation, which was fast in Na+-loaded cells, was strongly inhibited in Li+-loaded cells, despite high membrane potential and respiratory rate. When Li+-loaded cells were placed into medium containing Na+ instead of Li+, Li+/Na+ exchange took place initially, while K+ accumulation was delayed. Only after almost all inside Li+ was replaced by Na+ did active Na+ and K+ transport commence. These data confirm that it is a distinct active sodium transport system (AST) with Na+,K+/H+ antiporter activity, and not the Na+/H+ antiporters, that is responsible for active Na+ transport in E. coli [Verkhovskaya, M.L., Verkhovsky, M.I. and Wikstrom, M. (1996) Biochim. Biophys. Acta 1273, 207-216]. In contrast to the Na+/H+ antiporters, the AST system is inhibited by Li+.
Verkhovskaya
M L
ML
Helisinki Bioenegetics Group, Department of Medical Chemistry, Institute of Biomedical Sciences, University of Helsinki, Finland. verhovs@penger.helsinki.fi
Verkhovsky
M I
MI
Wikström
M
M
D001693:Biological Transport, Active; D004926:Escherichia coli / Q000378:metabolism*; D008094:Lithium / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D008094:Lithium; D012964:Sodium; D011188:Potassium