title: Active K+ transport in Mycoplasma mycoides var. Capri. Net and unidirectional K+ movements.
abstract: 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 (Na+i: 20 mM). Unlike Na+i,K+i 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, K+i 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.
mesh_terms: D001693:Biological Transport, Active / Q000187:drug effects; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D007700:Kinetics; D009176:Mycoplasma mycoides / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
chemical_list: D004024:Dicyclohexylcarbodiimide; D012964:Sodium; D005947:Glucose; D011188:Potassium