Dipple I, Gordon L M, Houslay M D
J Biol Chem. 1982 Feb 25;257(4):1811-5.
The 5'-nucleotidase activity of rat liver plasma membranes could be selectively modulated by the anionic drugs phenobarbital and pentobarbital, whereas the corresponding activity of a Lubrol-solubilized preparations remained unaltered. The perturbation in the outer half of the bilayer induced by phenobarbital, which lead to a depression in the high temperature onset of the lipid phase separation occurring in this half of the bilayer, concomitantly lowered the break temperature in Arrhenius plots of 5'-nucleotidase activity from 28 degrees C to 16 degrees C. The stimulation of the membrane-bound activity achieved by low anionic drug concentrations was attributed to a preferential fluidization of the outer half of the bilayer. Contrarily, the cationic drugs prilocaine and carbocaine, when tested over agent concentrations that dramatically increase the fluidity of the inner half of the bilayer, achieved no selective effects on the membrane-bound enzyme. Prilocaine (10 mM) was previously found to induce a lipid phase separation at 11 degrees C that was attributed to the lipids of the internal (cytosol-facing) half of the bilayer, but had no effect on the onset of the lipid phase separation occurring at 28 degrees C. Since Arrhenius plots of 5'-nucleotidase activity in the presence of 10 mM prilocaine concentrations demonstrated only the single break at 28 degrees C, we suggest that prilocaine is unable to selectively perturb the enzyme because this cationic drug preferentially interacts with the acidic phospholipids residing in the inner half of the bilayer. The activity of the ectoenzyme 5'-nucleotidase in rat liver plasma membranes appears to be regulated by the external half of the bilayer only. These results support the view that independent modulation of he fluidity or chemical constituents of each half of the bilayer can distinctly affect the activity of proteins that are themselves asymmetrically orientated within the bilayer.
大鼠肝细胞膜的5'-核苷酸酶活性可被阴离子药物苯巴比妥和戊巴比妥选择性调节，而用Lubrol增溶制剂的相应活性则保持不变。苯巴比妥引起双层膜外半部分的扰动，导致该半部分双层膜中脂质相分离的高温起始点降低，同时使5'-核苷酸酶活性的阿伦尼乌斯图中的转折温度从28℃降至16℃。低浓度阴离子药物对膜结合活性的刺激归因于双层膜外半部分的优先流化。相反，当在显著增加双层膜内半部分流动性的药物浓度下测试时，阳离子药物丙胺卡因和卡波卡因对膜结合酶没有选择性作用。先前发现丙胺卡因（10 mM）在11℃诱导脂质相分离，这归因于双层膜内部（面向胞质溶胶）半部分的脂质，但对28℃发生的脂质相分离起始点没有影响。由于在10 mM丙胺卡因浓度下5'-核苷酸酶活性的阿伦尼乌斯图仅显示在28℃有单一转折，我们认为丙胺卡因无法选择性地扰动该酶，因为这种阳离子药物优先与位于双层膜内半部分的酸性磷脂相互作用。大鼠肝细胞膜中外切酶5'-核苷酸酶的活性似乎仅受双层膜外半部分的调节。这些结果支持这样一种观点，即双层膜每一半的流动性或化学成分的独立调节可明显影响自身在双层膜中不对称取向的蛋白质的活性。
