ACTIVE-K+ TRANSPORT IN MYCOPLASMA-MYCOIDES VAR CAPRI - NET AND UNIDIRECTIONAL K-+ MOVEMENTS

Analysis of the cation composition of growing Mycoplasma mycoides var. Capri indicates that these organisms have a high intracellular K+ concentration (Ki: 200-300 mM) which greatly exceeds that of the growth medium, and a low Na+ concentration (Nai+: 20 mM). Unlike Nai+, Ki+ varies with cell aging. The K+ transport properties studied in washed organisms resuspended in buffered saline solution show that cells maintain a steady and large K+ concentration gradient across their membrane at the expense of metabolic energy mainly derived from glycolysis. In starved cells, Ki+ decreases and is partially compensated by a gain in Na+. This substitution completely reverses when metabolic substrate is added (K+ reaccumulation process). Kinetic analysis of K+ movement in cells with steady K+ level shows that most of K+ influx is mediated by an autologous K+-K+ exchange mechanism. On the other hand, during K+ reaccumulation by K+-depleted cells, a different mechanism (a K+ uptake mechanism) with higher transport capacity and affinity drives the net K+ influx. Both mechanisms are energy-dependent. Ouabain and anoxia have no effect on K+ transport mechanisms; in contrast, both processes are completely blocked by dicyclohexylcarbodiimide, an inhibitor of the Mg2+-dependent ATPase activity. © 1979.