Laboratório de Bioenergética e Fisiologia Mitocondrial, Programa de Biofísica e Bioquímica Celular, Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, CEP 21941-590, Brazil.
Biochem J. 2013 Jan 1;449(1):263-73. doi: 10.1042/BJ20120396.
NO (nitric oxide) is described as an inhibitor of plant and mammalian respiratory chains owing to its high affinity for COX (cytochrome c oxidase), which hinders the reduction of oxygen to water. In the present study we show that in plant mitochondria NO may interfere with other respiratory complexes as well. We analysed oxygen consumption supported by complex I and/or complex II and/or external NADH dehydrogenase in Percoll-isolated potato tuber (Solanum tuberosum) mitochondria. When mitochondrial respiration was stimulated by succinate, adding the NO donors SNAP (S-nitroso-N-acetyl-DL-penicillamine) or DETA-NONOate caused a 70% reduction in oxygen consumption rate in state 3 (stimulated with 1 mM of ADP). This inhibition was followed by a significant increase in the Km value of SDH (succinate dehydrogenase) for succinate (Km of 0.77±0.19 to 34.3±5.9 mM, in the presence of NO). When mitochondrial respiration was stimulated by external NADH dehydrogenase or complex I, NO had no effect on respiration. NO itself and DETA-NONOate had similar effects to SNAP. No significant inhibition of respiration was observed in the absence of ADP. More importantly, SNAP inhibited PTM (potato tuber mitochondria) respiration independently of oxygen tensions, indicating a different kinetic mechanism from that observed in mammalian mitochondria. We also observed, in an FAD reduction assay, that SNAP blocked the intrinsic SDH electron flow in much the same way as TTFA (thenoyltrifluoroacetone), a non-competitive SDH inhibitor. We suggest that NO inhibits SDH in its ubiquinone site or its Fe-S centres. These data indicate that SDH has an alternative site of NO action in plant mitochondria.
一氧化氮（NO）因其与细胞色素 c 氧化酶（COX）的高亲和力而被描述为植物和哺乳动物呼吸链的抑制剂，这阻碍了氧还原为水。在本研究中，我们表明，在植物线粒体中，NO 也可能干扰其他呼吸复合物。我们分析了用 Percoll 分离的土豆块茎（Solanum tuberosum）线粒体中的复合物 I 和/或复合物 II 和/或外部 NADH 脱氢酶支持的氧消耗。当线粒体呼吸被琥珀酸刺激时，添加 NO 供体 SNAP（S-亚硝基-N-乙酰-DL-青霉胺）或 DETA-NONOate 会导致 3 状态下的氧消耗率降低 70%（用 1 mM ADP 刺激）。这种抑制后，SDH（琥珀酸脱氢酶）对琥珀酸的 Km 值显著增加（在有 NO 的情况下为 0.77±0.19 至 34.3±5.9 mM）。当线粒体呼吸由外部 NADH 脱氢酶或复合物 I 刺激时，NO 对呼吸没有影响。NO 本身和 DETA-NONOate 对 SNAP 有类似的作用。在没有 ADP 的情况下，没有观察到呼吸的显著抑制。更重要的是，SNAP 独立于氧张力抑制 PTM（土豆块茎线粒体）呼吸，表明与在哺乳动物线粒体中观察到的不同的动力学机制。我们还在 FAD 还原测定中观察到，SNAP 以与 TTFA（全氟三氟丙酮）非常相似的方式阻断了内在的 SDH 电子流，TTFA 是一种非竞争性 SDH 抑制剂。我们认为，NO 抑制 SDH 的泛醌部位或其 Fe-S 中心。这些数据表明，SDH 在植物线粒体中有 NO 作用的替代部位。
