Chen L I, Chen C H
Arch Biochem Biophys. 1986 Dec;251(2):606-15. doi: 10.1016/0003-9861(86)90370-x.
To further consider the thermochemical method as a useful approach for active transport research and to investigate the characteristic of a proton electrochemical potential (delta mu H+) across the membrane, the energetics of lactose active transport across Escherichia coli membrane vesicles coupled with an artificial electron donor (phenazine methosulfate-ascorbate) has been investigated. The results were compared with those obtained with an enzyme-associated electron donor (lactate dehydrogenase-D-lactate). The oxidation of an electron donor provided the energy necessary for the transport process. The observed higher heat of ascorbate oxidation reaction in the presence of a proton ionophore (carbonyl cyanide m-chlorophenylhydrazone) further confirmed the formation of delta mu H+ across the membrane. Part of the oxidation energy was utilized to form delta mu H+. Comparison of the energetics revealed that the magnitudes of delta Hox (the enthalpy of the oxidation reaction) and delta Hm (the enthalpy of the formation of delta mu H+) in the two energy sources were comparable (-46 kcal/mol of ascorbate to -40 kcal/mol of D-lactate for delta Hox and 9.6 kcal/mol of ascorbate to 14 kcal/mol of D-lactate for delta Hm). Comparable and low value (about 1%) was also found in the free energy transfer (defined by delta Gm/delta Gox) from the oxidation reaction to the formation of delta mu H+. These results, in combination with the close values of delta mu H+ observed in the two systems, suggested that the characteristic of the created delta mu H+ was independent of the energy source. Examination of delta Hm might provide the information on the ratio of the number of protons produced, as 1 mol of two different electron donors was oxidized. The oxidation reaction in the presence of membrane vesicles was discussed.
为了进一步将热化学方法视为主动运输研究的一种有用方法，并研究跨膜质子电化学势（δμH⁺）的特性，我们研究了乳糖在大肠杆菌膜囊泡上的主动运输能量学，该过程与人工电子供体（吩嗪硫酸甲酯 - 抗坏血酸盐）偶联。将结果与使用酶相关电子供体（乳酸脱氢酶 - D - 乳酸）获得的结果进行了比较。电子供体的氧化提供了运输过程所需的能量。在质子离子载体（羰基氰化物间氯苯腙）存在下观察到的抗坏血酸氧化反应的较高热进一步证实了跨膜δμH⁺的形成。部分氧化能量用于形成δμH⁺。能量学比较表明，两种能量来源中δHox（氧化反应的焓）和δHm（δμH⁺形成的焓）的大小相当（抗坏血酸的δHox为 - 46 kcal/mol，D - 乳酸的为 - 40 kcal/mol；抗坏血酸的δHm为9.6 kcal/mol，D - 乳酸的为14 kcal/mol）。在从氧化反应到δμH⁺形成的自由能转移（由δGm/δGox定义）中也发现了相当且低值（约1%）。这些结果，结合在两个系统中观察到的δμH⁺的相近值，表明所产生的δμH⁺的特性与能量来源无关。检查δHm可能提供有关1摩尔两种不同电子供体被氧化时产生的质子数比例的信息。讨论了膜囊泡存在下的氧化反应。
