title: Temperature-dependent relationship between K+ influx, Mg2+-ATPase activity, transmembrane potential and membrane lipid composition in mycoplasma.
abstract: The temperature-dependent relationship between K+ active influx, Mg2+-ATPase activity, transmembrane potential (delta psi) and the membrane lipid composition has been investigated in mycoplasma PG3. Native organisms were grown in a medium containing 10 microgram/ml cholesterol and either oleic plus palmitic (chol (+), O + P) or elaidic (chol (+), E) acids. Adapted cells were grown in a medium free of exogenous cholesterol and supplemented with elaidic acid (chol (-), E). Arrhenius plots of 42K+ active influx gave a linear relationship for (chol (+), O + P) cells (EA = -9 kcal). On the other hand, when oleic plus palmitic acids are replaced by elaidic acid, an upward discontinuity appears between 28 and 30 degrees C, which is associated with a large increase in the apparent activation energy of the process (t > 30 degrees C, EA = -24 kcal; t < 30 degrees C, EA = -40 kcal). Finally, a biphasic response with a break at approx. 23 degrees C (EA = -7 kcal, t > 23 degrees C; EA = -44 kcal, t < 23 degrees C) is observed for (chol(-), E) organisms. From the lack of correspondence between these effects on the K+ influx and the temperature dependence of both the Mg2+-ATPase activity and delta psi, it is suggested that changes in the membrane lipid composition affect the K+ transport at the level of the K+ carrier itself. Differential scanning calorimetry, steady-state fluorescence polarization of diphenylhexatriene and freeze-fracture electron microscopy experiments further suggest that the effect is largely due to modifications of the membrane microviscosity and that the K+ carrier is associated with the most fluid lipid species present in the membrane.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D005614:Freeze Fracturing; D007700:Kinetics; D008563:Membrane Lipids / Q000378:metabolism*; D008564:Membrane Potentials; D009174:Mycoplasma / Q000378:metabolism* / Q000648:ultrastructure; D011188:Potassium / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics
chemical_list: D008563:Membrane Lipids; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D011188:Potassium