Three distinct cation/proton antiport systems have been characterized in L-form NC7 of
Escherichia coli K-12 by the effects of cations on the pH gradient established by oxidation of lactate or hydrolysis of Mg-ATP in everted membrane vesicles: potassium/proton, sodium/ proton and calcium/proton antiport systems. External pH value had significant effects on the Ca^<2+>/proton antiport process and the optimum pH laid in range of 7.5 to 8.0. The dissipation of ⊿pH, at pH 7.2, was dependent on the concentration of the externally added Ca^<2+>, and the saturation level was obtained at high concentration (about 10 mM) of Ca^<2+>, whereas at pH 8.0, it was independent on concentration over the range of 1 to 10 mM, and the saturation level was obtained at low Ca^<2+> concentration of about 1 mM.