质子载体解偶联剂和解偶联剂α,ω-十六烷二酸在静息态（状态4）下缓解了琥珀酸引起的谷氨酸和苹果酸氧化的阻断

摘要(中文译文)

理论和实验研究表明，在缺乏ATP合成的肝脏线粒体中（状态4），琥珀酸与谷氨酸和苹果酸混合物的氧化，如同单独氧化琥珀酸一样，在质子动力势的生成中仅涉及复合体III和IV，而不泵送质子的复合体II则氧化琥珀酸。因此，琥珀酸氧化抑制谷氨酸和苹果酸的氧化，可能是通过在复合体I处诱导反向电子传递（RET）并抑制NADH氧化来实现的。观察到琥珀酸对谷氨酸和苹果酸氧化阻断作用的半最大效应浓度为220 ± 25 µM，这与生理条件下各种器官和组织细胞中的浓度相对应。质子载体解偶联剂n-三氟甲氧基羰基氰基苯腙（FCCP）、棕榈酸（PA）和鹅去氧胆酸（CDCA），在其刺激呼吸不超过两倍的条件下，可减轻琥珀酸对谷氨酸和苹果酸氧化的抑制。解偶联剂α,ω-十六烷二酸（HDA）在刺激线粒体呼吸1.5倍的条件下，同样可减轻琥珀酸对谷氨酸和苹果酸氧化的抑制作用。值得注意的是，与质子载体解偶联剂不同，HDA的这一效应可能与呼吸链复合体III切换至空转模式有关。在谷氨酸和苹果酸氧化过程中，即正向电子传递条件下，质子载体解偶联剂FCCP、PA和CDCA抑制肝脏线粒体H₂O₂的生成，而HDA无效。在琥珀酸及琥珀酸与谷氨酸和苹果酸混合物氧化过程中，即反向电子传递（RET）条件下，质子载体解偶联剂和HDA对肝脏线粒体H₂O₂生成的抑制作用程度大致相同。推测上述解偶联剂和HDA的这一效应可能与抑制RET有关，从而减轻琥珀酸对谷氨酸和苹果酸氧化的抑制作用。本研究表明，生理浓度的琥珀酸足以主导电子流，而经典解偶联剂和天然解偶联剂以及解偶联剂HDA均可逆转这一效应，尽管其机制途径不同。

Abstract

Theoretical and experimental studies have revealed that in liver mitochondria in the absence of ATP synthesis (state 4), the oxidation of a mixture of succinate with glutamate and malate, like the oxidation of succinate alone, involves only complexes III and IV in the generation of the proton motive force, while complex II, which does not pump protons, oxidizes succinate. Consequently, succinate oxidation suppresses the oxidation of glutamate and malate, likely by inducing reverse electron transport (RET) at complex I and inhibiting NADH oxidation. The concentration of succinate at which its half-maximal effect on blocking glutamate and malate oxidation is observed is 220 ± 25 µM, which corresponds to its concentration in cells of various organs and tissues under physiological conditions. The protonophore uncouplers n-trifluoromethoxycarbonylcyanide phenylhydrazone (FCCP), palmitic acid (PA), and chenodeoxycholic acid (CDCA), provided that they stimulate respiration no more than two-fold alleviate the suppression of glutamate and malate oxidation by succinate. The decoupler α,ω-hexadecanedioic acid (HDA), upon stimulating mitochondrial respiration by 1.5-fold, also alleviates the suppressive effect of succinate on glutamate and malate oxidation. It is noted that, unlike protonophore uncouplers, this effect of HDA may be associated with switching complex III of the respiratory chain to an idle mode of operation. During the oxidation of glutamate and malate, i.e., under conditions of forward electron transport, the protonophore uncouplers FCCP, PA, and CDCA inhibit HO generation by liver mitochondria, whereas HDA is ineffective. During the oxidation of succinate and the mixture of succinate with glutamate and malate, i.e., under conditions of reverse electron transport (RET), protonophore uncouplers and HDA inhibit HO generation by liver mitochondria to approximately the same extent. It is suggested that this effect of the aforementioned uncouplers and HDA is likely related to the inhibition of RET and, consequently, to the alleviation of the suppressive effect of succinate on glutamate and malate oxidation. This study demonstrates that the physiological concentration of succinate is sufficient to dominate electron flow, and that both classical and natural uncouplers, as well as the decoupler HDA, can reverse this effect, albeit via different mechanistic pathways.

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