Becucci Lucia, Aloisi Giovanni, Guidelli Rolando
Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy.
Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy.
Bioelectrochemistry. 2017 Feb;113:51-59. doi: 10.1016/j.bioelechem.2016.10.001. Epub 2016 Oct 6.
Melittin exhibits an ohmic behavior in a lipid bilayer having a DOPC distal leaflet and interposed between a 2.25nm tetraethyleneoxy chain tethered to a mercury drop and an aqueous solution. This behavior is induced in a pH6.8 buffer solution of 0.8μg/mL melittin by a pretreatment consisting of series of electrochemical impedance spectroscopy measurements at bias potentials varied by 50mV steps over a transmembrane potential range from about +250 to -250mV. This metastable ohmic behavior remains unchanged for hours, even after acidifying the solution to pH3. The midpoint potential E between the positive and negative peaks of the resulting cyclic voltammogram is almost coincident with that of the ohmic channels gramicidin and syringopeptin 25A and shifts by the same amount toward more positive potentials with a pH decrease from 6.8 to 3. This common cyclic voltammetry behavior is explained by a tilt of the DOPC polar heads around the channel mouth of these three peptides and is simulated by a modelistic approach. The ohmic behavior of melittin is explained by the persistence of the peptide orientation initially assumed at trans-negative potentials even after application of trans-positive ones, at sufficiently high peptide-to-lipid molar ratios.
蜂毒肽在具有二油酰磷脂酰胆碱（DOPC）远端小叶的脂质双层中表现出欧姆行为，该脂质双层夹在连接到汞滴的2.25纳米四亚乙基氧基链和水溶液之间。这种行为是在0.8μg/mL蜂毒肽的pH6.8缓冲溶液中通过预处理诱导产生的，该预处理包括在跨膜电位范围约为+250至-250mV内以50mV步长变化的偏置电位下进行一系列电化学阻抗谱测量。这种亚稳的欧姆行为即使在将溶液酸化至pH3后仍能保持数小时不变。所得循环伏安图的正负峰之间的中点电位E几乎与欧姆通道短杆菌肽和丁香肽25A的中点电位一致，并且随着pH从6.8降至3，向更正的电位移动相同的量。这种共同的循环伏安行为是由DOPC极性头部围绕这三种肽的通道口倾斜来解释的，并通过模型方法进行模拟。蜂毒肽的欧姆行为是由即使在施加跨膜正电位后，在足够高的肽与脂质摩尔比下，最初在跨膜负电位下假设的肽取向的持续存在来解释的。
