Joseph-Horne T, Hollomon D W, Wood P M
Department of Biochemistry, School of Biomedical Sciences, University of Bristol, UK.
Biochim Biophys Acta. 2001 Apr 2;1504(2-3):179-95. doi: 10.1016/s0005-2728(00)00251-6.
In animals, electron transfer from NADH to molecular oxygen proceeds via large respiratory complexes in a linear respiratory chain. In contrast, most fungi utilise branched respiratory chains. These consist of alternative NADH dehydrogenases, which catalyse rotenone insensitive oxidation of matrix NADH or enable cytoplasmic NADH to be used directly. Many also contain an alternative oxidase that probably accepts electrons directly from ubiquinol. A few fungi lack Complex I. Although the alternative components are non-energy conserving, their organisation within the fungal electron transfer chain ensures that the transfer of electrons from NADH to molecular oxygen is generally coupled to proton translocation through at least one site. The alternative oxidase enables respiration to continue in the presence of inhibitors for ubiquinol:cytochrome c oxidoreductase and cytochrome c oxidase. This may be particularly important for fungal pathogens, since host defence mechanisms often involve nitric oxide, which, whilst being a potent inhibitor of cytochrome c oxidase, has no inhibitory effect on alternative oxidase. Alternative NADH dehydrogenases may avoid the active oxygen production associated with Complex I. The expression and activity regulation of alternative components responds to factors ranging from oxidative stress to the stage of fungal development.
在动物中，电子从NADH传递至分子氧是通过线性呼吸链中的大型呼吸复合体进行的。相比之下，大多数真菌利用分支呼吸链。这些分支呼吸链由交替NADH脱氢酶组成，它们催化对鱼藤酮不敏感的基质NADH氧化，或使细胞质NADH能够直接被利用。许多真菌还含有一种交替氧化酶，它可能直接从泛醇接受电子。少数真菌缺乏复合体I。尽管这些交替成分不参与能量守恒，但它们在真菌电子传递链中的组织确保了从NADH到分子氧的电子传递通常与质子通过至少一个位点的跨膜转运相偶联。交替氧化酶使呼吸作用能够在存在泛醇：细胞色素c氧化还原酶和细胞色素c氧化酶抑制剂的情况下继续进行。这对于真菌病原体可能特别重要，因为宿主防御机制通常涉及一氧化氮，虽然一氧化氮是细胞色素c氧化酶的有效抑制剂，但对交替氧化酶没有抑制作用。交替NADH脱氢酶可能避免与复合体I相关的活性氧产生。交替成分的表达和活性调节对从氧化应激到真菌发育阶段等多种因素作出反应。
