Marchal D, Boireau W, Laval J M, Moiroux J, Bourdillon C
Laboratoire de Technologie Enzymatique, Unité Associée au CNRS 1442, Université de Technologie de Compiègne, France.
Biophys J. 1997 Jun;72(6):2679-87. doi: 10.1016/S0006-3495(97)78911-2.
Physiological mole fractions of long isoprenic chain ubiquinone (UQ[10]) and plastoquinone (PQ9) were incorporated inside a supported bilayer by vesicle fusion. The template of the bilayer was an especially designed microporous electrode that allows the direct electrochemistry of water insoluble molecules in a water environment. The artificial structure, made by self-assembly procedures, consisted of a bilayer laterally in contact with a built-in gold electrode at which direct electron transfers between the redox heads of the quinones molecules and the electrode can proceed. The mass balances of quinone and lipid in the structure were determined by radiolabeling and spectrophotometry. A dimyristoyl phosphatdylcholine stable surface concentration of 250 +/- 50 pmol x cm(-2), unaffected by the presence of the quinone, was measured in the fluid monolayer. The mole fraction of quinone was between 1 and 3 mol%, remaining unchanged when going from the vesicles to the supported layers. The lipid molecules and the quinone pool were both laterally mobile, and cyclic voltammetry was used to investigate the redox properties of UQ10 and PQ9 over a wide pH range. Below pH 12, the two electrons-two protons electrochemical process at the gold electrode appeared under kinetic control. Thus all thermodynamic deductions must be anchored in the observed reversibility of the quinone/hydroquinol anion transformation at pH > 13. Within the experimental uncertainty, the standard potentials and the pK(a)'s of the pertinent redox forms of UQ10 and PQ9 were found to be essentially identical. This differs slightly from the literature in which the constants were deduced from the studies of model quinones in mixed solvents or of isoprenic quinones without a lipidic environment.
通过囊泡融合将长异戊二烯链泛醌（UQ[10]）和质体醌（PQ9）的生理摩尔分数掺入支撑双层膜内部。双层膜的模板是一种特别设计的微孔电极，它允许在水环境中对水不溶性分子进行直接电化学研究。通过自组装程序构建的人工结构由一个与内置金电极横向接触的双层膜组成，醌分子的氧化还原头与电极之间可以进行直接电子转移。通过放射性标记和分光光度法测定了结构中醌和脂质的质量平衡。在流体单层中测得二肉豆蔻酰磷脂酰胆碱的稳定表面浓度为250±50 pmol·cm⁻²，不受醌存在的影响。醌的摩尔分数在1%至3%之间，从囊泡转移到支撑层时保持不变。脂质分子和醌池在横向都是可移动的，循环伏安法用于研究UQ10和PQ9在较宽pH范围内的氧化还原性质。在pH 12以下，金电极上的双电子-双质子电化学过程受动力学控制。因此，所有热力学推导都必须基于在pH>13时醌/对苯二酚阴离子转化所观察到的可逆性。在实验误差范围内，发现UQ10和PQ9相关氧化还原形式的标准电位和pK(a)基本相同。这与文献略有不同，文献中的常数是从混合溶剂中模型醌或无脂质环境的异戊二烯醌的研究中推导出来的。
