An EPR analysis of cyanide-resistant mitochondria isolated from the mutant poky strain of Neurospora crassa.

An analysis of the paramagnetic components present in mitochondria isolated from the poky mutant of Neurospora crassa is described. The study was undertaken with a view to shedding light on the nature of the cyanide- and antimycin A-resistant alternative terminal oxidase which is present in these preparations. Of the ferredoxin-type iron-sulfure centers, only Centers S-1 and S-2 of succinate dehydrogenase could be detected in significant quantities. Paramagnetic centers attributable to Site I were virtually absent. In the oxidized state, at least two 'high potential iron sulfur' centers could be distinguished and these were attributed to Center S-3 of succinate dehydrogenase and a second component analogous to that found in mammalian systems. Much of the Center S-3 signal was in a highly distorted state which was apparently dependent upon the presence of an accompanying free radical species. At lower field positions, a succinate-reducible signal peaking around g = 3.15 was found. This signal is caused by a low spin heme species, presumably the cytochrome c which is the only major cytochrome in these mitochondria. At even lower field positions, signals attributable to iron in a field of low symmetry at g = 4.3 and multiple high spin heme species around g = 6, could be distinguished. The effects of salicylhydroxamic acid, an inhibitor of the alternative oxidase, were tested on these components. Effects could be seen on at least one high spin heme component and also partially upon the distorted Center S-3 signal converting part of it to a signal indistinguishable from center S-3. Some increase in the g = 4.3 iron signal was also noted. No effects of the inhibitor on the ferredoxin-type centers were detected.