Electron spin resonance investigations of mitochondrial electron transport in Neurospora crassa. Characterization of paramagnetic intermediates in a standard strain.

1. Submitochondrial particles from Neurospora strain inl-89601 have been analyzed by electron spin resonance spectroscopy (ESR). Numerous signals due to iron-sulfur proteins are observed at low temperatures. Analysis of these ESR signals at various temperatures allows the assignment of resonances to iron-sulfur centers 1-5 that have been described in other organisms. There are no discrepancies between the signals seen in Neurospora and those described in other organisms and it is likely that Neurospora mitochondria contain the same iron-sulfur centers that are observed elsewhere. 2. NADPH and NADH act to reduce the iron-sulfur centers of respiratory complex I. 3. The drug pyrrolnitrin [3-chloro-4-(2'-nitro-3'-chlorphenyl)pyrrole] is an effective inhibitor of both NADH-supported and succinate-supported electron transport in Neurospora. 4. Analysis of pyrrolnitrin inhibition curves, respiration studies, ESR spectra, and the steady-state level of reduction of cytochrome b in the presence and absence of the drug shows that pyrrolnitrin acts to inhibit electron transport in Neurospora mitochondria at multiple sites in the region between ubiquinone and cytochrome b.