Nohl H, Schönheit K
Institute of Pharmacology and Toxicology, Veterinary University of Vienna, Josef Baumanngasse 1, Vienna, A-1210, Austria.
Arch Biochem Biophys. 1996 Jul 15;331(2):259-64. doi: 10.1006/abbi.1996.0306.
Heart mitochondria can be made to oxidize extramitochondrial NADH via the exogenous NADH dehydrogenase. Oxidation of extramitochondrial NADH was found to be associated with the disappearance of H+ from the suspension medium. Our studies on the possible pathway through which H+ may disappear from the extramitochondrial space were focused on (i) an unspecific transmembranous H+ leakage along the electrochemical H+ gradient following peroxidative membrane alteration, (ii) stimulation of a controlled H+ reconduction through the H+ channel of the ATP synthase, and (iii) stimulation of the Na+/H+ counterporter by Ca2+ release. Our experiments revealed that none of these H+ pathways was involved in the observed alkalinization of the extramitochondrial space during respiration of external NADH. The latter effect was inhibited when oxidation of external NADH via the respiratory chain was blocked and could be turned into the opposite when artificial e- acceptors of the exogenous NADH dehydrogenase were used to reactivate NADH consumption. Stoichiometric analysis of H+ disappearance and O2 consumption revealed that reducing equivalents of external NADH were transferred to oxygen via cytochrome oxidase and H+ from the suspension was used to release water.
心脏线粒体可通过外源性NADH脱氢酶氧化线粒体外的NADH。发现线粒体外NADH的氧化与悬浮介质中H⁺的消失有关。我们对H⁺可能从线粒体外空间消失的潜在途径的研究集中在：（i）在过氧化膜改变后，H⁺沿着电化学H⁺梯度进行非特异性跨膜泄漏；（ii）通过ATP合酶的H⁺通道刺激可控的H⁺再传导；（iii）Ca²⁺释放刺激Na⁺/H⁺反向转运体。我们的实验表明，在外部NADH呼吸过程中观察到的线粒体外空间碱化现象中，这些H⁺途径均未参与。当通过呼吸链氧化外部NADH被阻断时，后一种效应受到抑制，而当使用外源性NADH脱氢酶的人工电子受体重新激活NADH消耗时，该效应可能会反转。对H⁺消失和O₂消耗的化学计量分析表明，外部NADH的还原当量通过细胞色素氧化酶转移到氧气中，悬浮液中的H⁺用于生成水。
