Balasubramanian K, Gupta C M
Institute of Microbial Technology, Chandigarh, India.
Eur J Biochem. 1996 Sep 15;240(3):798-806. doi: 10.1111/j.1432-1033.1996.0798h.x.
Aminophospholipid movements in the plasma membrane of higher eukaryotic cells seem to be regulated by an ATP-dependent, protein-mediated process. To examine whether similar mechanisms exist in yeast cells, we have analysed phosphatidylethanolamine (PtdEtn) distributions in Saccharomyces cerevisiae (A184D) cells under a variety of conditions, with trinitrobenzenesulfonic acid and fluorescamine as the external membrane probes. The levels of external PtdEtn in the intact cells were reduced to about 50% by pretreatment of the cells with inhibitors of mitochondrial ATP synthesis, ATPase inhibitors or protein-sulfhydryl-group-modifying reagents, or by depletion of the cells of ATP by metabolic starvation. The levels of external PtdEtn could be restored to normal by repletion of the energy-depleted cells with ATP. Furthermore, treatment of the energy-depleted cells with sulfhydryl-modifying reagents did not cause further reduction in the external PtdEtn levels but decreased the accessibility of PtdEtn to fluorescamine after restoration of the cellular ATP levels to normal in these cells. These results demonstrate an involvement of an ATP-dependent, protein-mediated process(es) in the regulation of the PtdEtn distribution across the plasma-membrane bilayer of yeast cells. The results are discussed with regard to possible models that can generate and maintain the transbilayer phospholipid asymmetry in the yeast plasma membrane.
高等真核细胞质膜中的氨基磷脂运动似乎受一种ATP依赖的、蛋白质介导的过程调控。为了研究酵母细胞中是否存在类似机制，我们使用三硝基苯磺酸和荧光胺作为外膜探针，分析了酿酒酵母（A184D）细胞在各种条件下磷脂酰乙醇胺（PtdEtn）的分布情况。用线粒体ATP合成抑制剂、ATP酶抑制剂或蛋白质巯基修饰试剂预处理细胞，或通过代谢饥饿耗尽细胞内的ATP，均可使完整细胞中外源PtdEtn的水平降低至约50%。用ATP补充能量耗尽的细胞，可使外源PtdEtn的水平恢复正常。此外，用巯基修饰试剂处理能量耗尽的细胞，不会导致外源PtdEtn水平进一步降低，但在这些细胞的细胞ATP水平恢复正常后，会降低PtdEtn与荧光胺的可及性。这些结果表明，ATP依赖的、蛋白质介导的过程参与了酵母细胞质膜双层中PtdEtn分布的调控。我们还讨论了关于可能在酵母质膜中产生和维持跨膜磷脂不对称性的模型的相关结果。
