Kaback H R, Ramos S, Robertson D E, Stroobant P, Tokuda H
J Supramol Struct. 1977;7(3-4):443-61. doi: 10.1002/jss.400070315.
Bacterial membrane vesicles retain the same sidedness as the membrane in the intact cell and catalyze active transport of many solutes by a respiration-dependent mechanism that does not involve the generation of utilization of ATP or other high-energy phosphate compounds. In E. coli vesicles, most of these transport systems are coupled to an electrochemical gradient of protons (deltamuH+, interior negative and alkaline) generated primarily by the oxidation of D-lactate or reduced phenazine methosulfate via a membrane-bound respiratory chain. Oxygen or, under appropriate conditions, fumarate or nitrate can function as terminal electron acceptors, and the site at which deltamuH+ is generated is located before cytochrome b1 in the respiratory chain. Certain (N-dansyl)aminoalkyl-beta-D-galactopyranosides (Dns-gal) and N(2-nitro-4-azidophenyl)aminoalkyl 1-thio-beta-D-galactopyranosides (APG) are competitive inhibitors of lactose transport but are not transported themselves. Various fluorescence techniques, direct binding assays, and photoinactivation studies demonstrate that the great bulk of the lac carrier protein (ca. 95%) does not bind ligand in the absence of energy-coupling. Upon generation of a deltamuH+ (interior negative and alkaline), binding of Dns-gal and APG-dependent photoinactivation are observed. The data indicate that energy is coupled to the initial step in the transport process, and suggest that the lac carrier protein may be negatively charged.
细菌膜囊泡保持与完整细胞中膜相同的不对称性，并通过一种不涉及ATP或其他高能磷酸化合物生成或利用的呼吸依赖机制催化多种溶质的主动运输。在大肠杆菌囊泡中，这些运输系统大多与质子的电化学梯度（ΔμH⁺，内部为负且呈碱性）偶联，该梯度主要由D-乳酸或还原型吩嗪硫酸甲酯通过膜结合呼吸链氧化产生。氧气或在适当条件下的富马酸或硝酸盐可作为末端电子受体，产生ΔμH⁺的位点位于呼吸链中细胞色素b1之前。某些（N-丹磺酰基）氨基烷基-β-D-吡喃半乳糖苷（Dns-gal）和N-（2-硝基-4-叠氮基苯基）氨基烷基1-硫代-β-D-吡喃半乳糖苷（APG）是乳糖运输的竞争性抑制剂，但它们自身不被运输。各种荧光技术、直接结合测定和光灭活研究表明，在没有能量偶联的情况下，大部分乳糖载体蛋白（约95%）不结合配体。在产生ΔμH⁺（内部为负且呈碱性）后，观察到Dns-gal的结合和APG依赖性光灭活。数据表明能量与运输过程的初始步骤偶联，并表明乳糖载体蛋白可能带负电荷。
