Cation transport and electrogenesis byStreptococcus faecalis

• DOI: 10.1007/bf01868093
• Publication Date: 2005-07-07T11:05:32Z
• Authors: F. M. Harold; D. Papineau
• Keywords: Valinomycin; Nigericin; Monensin

Uptake of the lipid-soluble cations dibenzyldimethylammonium (DDA+) and triphenylmethylphosphonium (TPMP+) byStreptococcus faecalis is biphasic. The initial phase is a rapid binding of the ions which does not require a source of metabolic energy and apparently consists of cation exchange at the cell surface. Upon addition of glucose further uptake of the cations occurs, by exchange for Na+ and H+. Evidence is presented suggesting that this metabolic uptake of DDA+ and TPMP+ is not due to active transport. It rather appears that uptake results from the generation of an electrical potential, interior negative, by the extrusion of H+ and, indirectly, of Na+. Accumulated DDA+ and TPMP+ are discharged by proton-conducting uncouplers. The cationconducting antibiotics valinomycin, monactin, nigericin and monensin do not inhibit uptake. Potassium and, under certain conditions, H+ displace DDA+ and TPMP+. Generation of an electrical difference across the membrane was verified by the accumulation of K+ in the presence of valinomycin. The concentration ratios achieved correspond to potentials of the order of −150 to −200 mV.