Maurel P, Douzou P, Waldmann J, Yonetani T
Biochim Biophys Acta. 1978 Aug 7;525(2):314-24. doi: 10.1016/0005-2744(78)90226-7.
The activity vs. pH profile for the oxidation of ferrocytochrome c by purified cytochrome oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) was investigated as a function of ionic strength (from 10 to 200 mM) in the absence and in the presence of various perturbants: Tween 20, linear polyanions (RNA, heparin, polyglutamic acid) and phospholipids (asolectin, phosphatidylcholine, phosphatidic acid and cardiolipin). The activation induced by Tween 20 and "zero net charge" phospholipid liposomes was not pH dependent. On the other hand, linear polyanions and polyanionic liposomes strongly perturbed the pH profile, mostly at low ionic strength, by shifting the pH optimum about 1.7 pH units towards alkaline pH values. This effect was reversed by increasing ionic strength. These observations are interpreted in the light of polyelectrolyte theory. Since these results show striking with membrane-bound enzyme, it is concluded that in vivo cytochrome oxidase is located within polyanionic sites of the micochondrial membrane. The activation broght about by phospholipids may result from two posible processes: creation of a hydrophobic environment by the non-polar tails, preventing autoaggregation; and creation of a suitable polyelectrolytic environment by the polar heads (of non zero net charge), increasing the intrinsic reaction rate.
在不存在和存在各种干扰剂（吐温20、线性聚阴离子（RNA、肝素、聚谷氨酸）和磷脂（大豆卵磷脂、磷脂酰胆碱、磷脂酸和心磷脂））的情况下，研究了纯化的细胞色素氧化酶（亚铁细胞色素c：氧氧化还原酶，EC 1.9.3.1）氧化亚铁细胞色素c的活性与pH的关系曲线随离子强度（从10到200 mM）的变化。吐温20和“零净电荷”磷脂脂质体诱导的激活不依赖于pH。另一方面，线性聚阴离子和聚阴离子脂质体在低离子强度下强烈干扰pH曲线，通过将最适pH向碱性pH值方向移动约1.7个pH单位。增加离子强度可逆转这种效应。根据聚电解质理论对这些观察结果进行了解释。由于这些结果与膜结合酶的情况惊人地相似，因此得出结论，体内细胞色素氧化酶位于线粒体膜的聚阴离子位点内。磷脂引起的激活可能源于两个可能的过程：非极性尾部形成疏水环境，防止自聚集；极性头部（非零净电荷）形成合适的聚电解质环境，提高内在反应速率。
