Shen X M, Li H, Dryhurst G
Department of Chemistry and Biochemistry, University of Oklahoma, Norman 73019, USA.
J Neural Transm (Vienna). 2000;107(8-9):959-78. doi: 10.1007/s007020070045.
A characteristic change in the substantia nigra of Parkinson's disease patients is an apparent accelerated rate of dopamine oxidation as evidenced by an increased 5-S-cysteinyldopamine (5-S-CyS-DA) to dopamine ratio. However, 5-S-CyS-DA is more easily oxidized than dopamine to give 7-(2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1,4-benzothiazine-3-carboxylic acid (DHBT-1). Previous studies have demonstrated that DHBT-1 can be accumulated by intact rat brain mitochondria and inhibits complex I but not complex II respiration. In this study, it is shown that DHBT-1 also inhibits the alpha-ketoglutarate dehydrogenase complex (alpha-KGDH) but not cytochrome c oxidase (complex IV). The inhibition of alpha-KGDH is dependent on the oxidation of DHBT-1, catalyzed by an unknown constituent of the inner mitochondrial membrane, to an electrophilic o-quinone imine that covalently modifies active site sulfhydryl residues. The latter conclusion is based on the ability of > or = equimolar glutathione to block the inhibition of alpha-KGDH by DHBT-1, without altering its rate of mitochondrial membrane-catalyzed oxidation, by scavenging the electrophilic o-quinone intermediate forming glutathionyl conjugates which have been isolated and spectroscopically characterized. Activities of mitochondrial alpha-KGDH and complex I, but not other respiratory complexes, are decreased in the parkinsonian substantia nigra. Such changes together with evidence for accelerated dopamine oxidation, increased formation of 5-S-CyS-DA and the ease of oxidation of this conjugate to DHBT-1 which inhibits alpha-KGDH and complex I, without affecting other respiratory enzyme complexes, suggests that the latter putative metabolite might be an endotoxin that contributes to the alpha-KGDH and complex I defects in Parkinson's disease.
帕金森病患者黑质的一个特征性变化是多巴胺氧化速率明显加快，这表现为5-S-半胱氨酰多巴胺（5-S-CyS-DA）与多巴胺的比率增加。然而，5-S-CyS-DA比多巴胺更容易被氧化，生成7-(2-氨基乙基)-3,4-二氢-5-羟基-2H-1,4-苯并噻嗪-3-羧酸（DHBT-1）。先前的研究表明，完整的大鼠脑线粒体可以积累DHBT-1，并且它抑制复合体I的呼吸作用，但不抑制复合体II的呼吸作用。在本研究中，结果表明DHBT-1还抑制α-酮戊二酸脱氢酶复合体（α-KGDH），但不抑制细胞色素c氧化酶（复合体IV）。α-KGDH的抑制作用取决于线粒体内膜一种未知成分催化的DHBT-1氧化，生成亲电的邻醌亚胺，该邻醌亚胺共价修饰活性位点的巯基残基。后一结论基于以下事实：≥等摩尔的谷胱甘肽能够通过清除形成谷胱甘肽共轭物的亲电邻醌中间体来阻断DHBT-1对α-KGDH的抑制作用，而不改变其线粒体膜催化的氧化速率，这些谷胱甘肽共轭物已被分离并进行了光谱表征。帕金森病患者黑质中线粒体α-KGDH和复合体I的活性降低，但其他呼吸复合体的活性未降低。这些变化以及多巴胺氧化加速、5-S-CyS-DA生成增加以及该共轭物易于氧化为抑制α-KGDH和复合体I而不影响其他呼吸酶复合体的DHBT-1的证据表明，后一种假定的代谢产物可能是一种内毒素，它导致了帕金森病中α-KGDH和复合体I的缺陷。
