The Properties of Citrate Transport in Membrane Vesicles from Bacillus subtilis
Open Access
- 1 July 1983
- journal article
- research article
- Published by Wiley in European Journal of Biochemistry
- Vol. 134 (1), 151-156
- https://doi.org/10.1111/j.1432-1033.1983.tb07545.x
Abstract
The uptake system for citrate is induced in Bacillus subtilis W23 by growth in the presence of citrate and only membrane vesicles isolated from these cells show energy-dependent citrate uptake. Citrate transport in membrane vesicles is strictly dependent on the presence of divalent cations such as Mg2+, Mn2+, Zn2+, Ba2+, Be2+, Ca2+, Cu2+, Co2+, or Ni2+. The initial rate of citrate transport increases with the divalent cation concentration up to a maximum. The maximum initial rate of citrate uptake is reached with 2 mM Mg2+. The cations form stable chelates with citrate. The metal citrate complex is the transported solute. This is demonstrated for citrate uptake in the presence of Ca2+. Membrane vesicles from citrate-grown cells accumulate Ca2+ and citrate only if both solutes are present. Citrate and Ca2+ are accumulated in equimolar quantities. The uptake of Ca2+ but not of citrate is inhibited by Mg2+. Uptake of the metal-citrate complex is inhibited by the uncoupler carbonylcyanide p-trifluoromethoxyphenyl-hydrazone and in the presence of K+ ions by valinomycin and nigericin. The inhibitory effects correlate with the effects observed on the components of the proton-motive force, indicating that the proton-motive force is a driving force for metal-citrate transport. The number of protons (n) symported with the metal-citrate complex has been determined under different experimental conditions from the steady state levels of citrate accumulation, the electrical potential and pH gradient. This number varies from 1 at pH 4.7 to 2 at pH 8.0.This publication has 31 references indexed in Scilit:
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