Effects of Phospholipid Acyl Chain Fluidity, Phase Transitions, and Cholesterol on (Na+ + K+)-stimulated Adenosine Triphosphatase

摘要: A soluble delipidized (Na + K)-stimulated ATPase was obtained from rabbit kidney outer medulla by the use of sodium deoxycholate. The activity this enzyme stimulated 20-fold to an 100 120 µmoles Pi per mg protein hour either phosphatidylserine or phosphatidylglycerol. effect fluidity hydrocarbon region phospholipid bilayers on re-activation K)-ATPase systematically examined. Fatty acyl chains known length and varying saturation were substituted phosphatidylglycerol moiety influence temperature degree investigated. Discontinuities in Arrhenius plots found compared with gel-to-liquid-crystalline transitions these phosphatidylglycerols as measured a differential scanning calorimeter. at which plot discontinuities occurred 1° 8° lower than initial rise main endothermic peak for series: dimyristoyl-, dipalmitoyl-, distearoylphosphatidylglycerols. Dioleoyl-phosphatidylglycerol does not undergo phase transition within experimental range activate much concentrations saturated phosphatidylglycerols, did show discontinuities. In contrast, bovine brain heterogeneous fatty chain composition showed discontinuity 2° higher midpoint broad peak. relation between lipid is discussed. It suggested that some represent completion melting (upper limit transition), whereas others beginning (lower limit). For completely liquid membranes, slopes are parallel give activation energy approximately 15 Cal mole. membrane also studied examining effects cholesterol constant (37°). agreement above findings, cholesterol, reduce chains, inhibits phospholipid-stimulated activity. inhibition complete, however, only phospholipids. Partial unsaturated These results discussed biomembranes membrane-bound enzymes. role controlling enzymes suggested. Implications protein-lipid interactions membranes considered.