Selective inhibition of antimycin A-insensitive respiration in Ustilago maydis and Ceratocystis ulmi

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Sporidia of Ustilago maydis and conidia of Ceratocystis ulmi possess an antimycin A and azide-tolerant electron transport pathway which apparently diverts electrons to O_2 from some point on the substrate side of the antimycin A block. The alternate pathway (induced by 0.5 μg/ml antimycin A or 5 × 10^<-4> M sodium azide) supports a respiratory rate 1.5-2 times that of the normal system, but has a terminal oxidase with a lower than normal affinity for O_2. A similarly high respiratory rate in U. maydis is supported by the normal pathway when uncoupled by 4 μg/ml of 4,5-dichloro-2-trifluoromethylbenzimidazole, but a ,high affinity for O_2 in this case indicates that the normal terminal oxidase is utilized. Respiration by the normal pathway in both fungi is only slightly or moderately inhibited by 1.5 × 10^<-3> M benzohydroxamic acid (BHAM) and 5 × 10^<-4> M 8-hydroxyquinoline. The alternate pathway in U. maydis, however, is inhibited as much as 84 and 92% respectively by these two compounds, while alternate respiration in C. ulmi can be inhibited as much as 86 and 76% respectively. BHAM, 8-hydroxyquinoline, 2-pyridinethiol-1-oxide, a,a'-dipyridyl, carboxin, and diphenylamine inhibit alternate respiration at a site on the alternate pathway which is not part of the normal electron transport system. Antimycin A and azide-insensitive respiration found in U. maydis and C. ulmi closely resembles inhibitor insensitivity noted in several fungi and some higher plants. Such an alternate respiratory pathway may be an early step in the evolution of oxidative phosphorylation.
日本植物生理学会の論文

Selective inhibition of antimycin A-insensitive respiration in Ustilago maydis and Ceratocystis ulmi

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