Cation transport and metabolism in Streptococcus fecalis
1.1. Streptococcus fecalis maintains an intracellular K+ concentration of 559 mM and an intracellular Na+ concentration of less than 5 mM when growing exponentially in a medium containing 4.6 mM K+ and 151 mM Na+. Cells harvested from the stationary phase are K+-poor and Na+-rich.2.2. An energy-dependent net uptake of K+ is observed following resuspension of K+-poor, Na+-rich cells in a neutral medium containing both substrate and K+.3.3. Net K+ uptake under these conditions is the result of two cation-exchange processes: (i) a K+−Na+ exchange which accounts for aapprox. 60% of the total K+ uptake; and, (ii) a K+−H+ exchange utilizing H+ present in the cell at the time of harvesting.4.4. Net cation transport is absolutely dependent on the metabolism of exogenous substrate, and both glucose and arginine will support the process, though at significantly different rates. With either substrate, the initial rate of net K+ uptake is equal to the calculated rate of ATP production.5.5. A transient two-fold increase in the glycolytic rate is closely associated with the onset of K+ uptake indicating a coupling between active cation transport and energy-yielding processes in this organism.