Chen L I, Chen C H
Arch Biochem Biophys. 1986 May 1;246(2):515-24. doi: 10.1016/0003-9861(86)90306-1.
The energetics of D-lactate-driven active transport of lactose in right-side-out Escherichia coli membrane vesicles has been investigated with a microcalorimetric method. Changes of enthalpy (delta Hox), free energy (delta Gox), and entropy (delta Sox) during the D-lactate oxidation reaction in the presence of membrane vesicles are -39.9 kcal, -46.4 kcal, and 22 cal/deg per mole of D-lactate, respectively. The free energy released by this reaction is utilized to form a proton electrochemical potential (delta-microH+) across the membrane. The higher observed heat in the D-lactate oxidation reaction in the presence of carbonylcyanide m-chlorophenylhydrazone (a proton ionophore) supports the postulate that delta-microH+ is formed across the membrane vesicles. Thermodynamic quantities for the formation of delta-microH+ are delta Hm = 14.1 kcal, delta Gm = 0.6 kcal, and delta Sm = 45 cal/deg per mole of D-lactate. The efficiency in the free energy transfer from the oxidation reaction to the formation of delta-microH+ (defined by delta Gm/delta Gox) was 2%, as compared to that in the heat transfer (defined by delta Hm/delta Hox) of 35%. The energetics of the movement of lactose in symport with proton across the membrane as a consequence of the formation of delta-microH+ are delta H1 = -19 kcal, delta G1 = -0.5 kcal, and delta S1 = -62 cal/deg per mole of lactose. No heat of reaction is contributed by lactose movement across the membrane without symport with H+.
采用微量量热法研究了D - 乳酸驱动乳糖在右侧外翻的大肠杆菌膜囊泡中进行主动运输的能量学。在膜囊泡存在的情况下，D - 乳酸氧化反应过程中的焓变（ΔHox）、自由能变（ΔGox）和熵变（ΔSox）分别为每摩尔D - 乳酸 - 39.9千卡、 - 46.4千卡和22卡/度。该反应释放的自由能用于在膜上形成质子电化学势（ΔμH⁺）。在羰基氰化物间氯苯腙（一种质子离子载体）存在下，D - 乳酸氧化反应中观察到的较高热量支持了在膜囊泡上形成ΔμH⁺的假设。形成ΔμH⁺的热力学量为每摩尔D - 乳酸ΔHm = 14.1千卡、ΔGm = 0.6千卡和ΔSm = 45卡/度。从氧化反应到形成ΔμH⁺的自由能转移效率（由ΔGm/ΔGox定义）为2%，而热传递效率（由ΔHm/ΔHox定义）为35%。由于形成了ΔμH⁺，乳糖与质子同向转运穿过膜的能量学参数为每摩尔乳糖ΔH1 = - 19千卡、ΔG1 = - 0.5千卡和ΔS1 = - 62卡/度。乳糖在不与H⁺同向转运的情况下穿过膜时不产生反应热。
