Non-proton-motive-force-dependent sodium efflux from the ruminal bacterium Streptococcus bovis: bound versus free pools.
AUTOR(ES)
Strobel, H J
RESUMO
Growing cells of Streptococcus bovis JB1 had a sodium content of 1,125 nmol/mg of protein and, based on a ratio of cell volume to protein of 4.3 microliters/mg, the apparent intracellular sodium concentration was more than 240 mM. Much of this sodium could not be removed by water washing even if cells were boiled or treated with the pore-forming ionophore, gramicidin, but it could be exchanged for potassium. Stationary cultures had a 2.6-microliters volume per milligram of protein and a total sodium content of 410 mM. When stationary cultures were energized with glucose at pH 6 to 8, sodium (more than 200 mM) was expelled within 2 min, and it appeared that growing cells had a very small pool of free intracellular sodium. Sodium-proton antiport activity could not be demonstrated with a sodium pulse, and the protonophore SF6847, valinomycin, and the H+-ATPase inhibitor dicyclohexylcarbodiimide (DCCD) had little effect on sodium efflux, even though these inhibitors greatly reduced the proton-motive force. SF6847, valinomycin, and DCCD had little effect on intracellular ATP, but iodoacetate, an inhibitor of glycolysis, decreased ATP as well as sodium efflux. Stationary cells from sodium-deficient medium expelled little sodium after glucose addition and had 35% more ATP than stationary cells which were grown in sodium medium and expelled sodium. An artificial electrochemical gradient of sodium was able to drive ATP synthesis in stationary cells, and this ATP formation was not sensitive to DCCD. These results indicated that bacteria could have a significant pool of bound sodium and that sodium expulsion from S. bovis was directly coupled to ATP hydrolysis.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=203141Documentos Relacionados
- Transport of amino acids in Lactobacillus casei by proton-motive-force-dependent and non-proton-motive-force-dependent mechanisms.
- Effect of extracellular pH on growth and proton motive force of Bacteroides succinogenes, a cellulolytic ruminal bacterium.
- Proton Motive Force During Growth of Streptococcus lactis Cells
- Sodium-dependent transport of neutral amino acids by whole cells and membrane vesicles of Streptococcus bovis, a ruminal bacterium.
- Low-affinity, high-capacity system of glucose transport in the ruminal bacterium Streptococcus bovis: evidence for a mechanism of facilitated diffusion.