Santhamma K R, Bhaduri A
Indian Institute of Chemical Biology, Calcutta.
Mol Biochem Parasitol. 1995 Dec;75(1):43-53. doi: 10.1016/0166-6851(95)02510-3.
Inhibition analysis of respiration of Leishmania donovani promastigotes in resting, starved and permeabilized cells in the presence of classical electron transfer complex inhibitors such as rotenone, thenoyltrifluoroacetone and antimycin demonstrated the absence of complex I component of the respiratory chain in this organism. Cyanide failed to completely block the oxygen uptake (residual 25-30%) even at high concentrations. The alternative oxidase inhibitor for Trypanosoma brucei, salicylhydroxamic acid (SHAM) had no effect on respiration while the cytochrome o inhibitor orthohydroxydiphenyl (OHD) could block cyanide-insensitive respiration at low concentrations. Succinate-dependent O2 uptake in permeabilized cells follows the classical pathway. Oxidation of NADH by a membrane-rich fraction produced H2O2 as the end product and was insensitive to respiratory chain inhibitors. The presence of NADH-fumarate reductase was demonstrated in membrane-rich fraction and fumarate could reduce H2O2 production from NADH indicating fumarate to be an endogenous substrate for accepting electrons from NADH. A differential route for NADH oxidation was further confirmed by NADH cytochrome c reductase insensitivity to antimycin. A tentative scheme for electron transfer pathway in this organism is proposed in which a reversal of Krebs cycle enzymes occur producing succinate that can be excreted or oxidized depending upon the energy demands of the cell. Inhibition studies also suggest bifurcations of the respiratory chain that can be of minor importance for the organism.
在存在鱼藤酮、噻吩甲酰三氟丙酮和抗霉素等经典电子传递复合物抑制剂的情况下，对静止、饥饿和通透细胞中的杜氏利什曼原虫前鞭毛体的呼吸抑制分析表明，该生物体中不存在呼吸链的复合物I成分。即使在高浓度下，氰化物也未能完全阻断氧气摄取（残留25%-30%）。布氏锥虫的替代氧化酶抑制剂水杨羟肟酸（SHAM）对呼吸没有影响，而细胞色素o抑制剂邻羟基二苯基（OHD）在低浓度时可阻断氰化物不敏感的呼吸。通透细胞中琥珀酸依赖性的氧气摄取遵循经典途径。富含膜的部分将NADH氧化产生H2O2作为终产物，并且对呼吸链抑制剂不敏感。在富含膜的部分中证实存在NADH-延胡索酸还原酶，延胡索酸可减少NADH产生的H2O2，表明延胡索酸是接受NADH电子的内源性底物。NADH细胞色素c还原酶对抗霉素不敏感进一步证实了NADH氧化的不同途径。提出了该生物体电子传递途径的暂定方案，其中克雷布斯循环酶发生逆转，产生琥珀酸，琥珀酸可根据细胞的能量需求排出或氧化。抑制研究还表明呼吸链存在分支，这对该生物体可能不太重要。
