The cytochrome oxidase inhibitor azide also inhibits the alternative pathway of Neurospora crassa

Mutant strains of Neurospora crassa were used to investigate the effects of the inhibitor azide upon respiration mediated by either the cyanide-insensitive alternative mitochondrial respiratory pathway or the "standard" cyanide-sensitive cytochrome pathway. The use of appropriate cytochrome-oxidase-deficient and alternative-oxidase-deficient mutants permitted respiration to be restricted to the pathway of choice. In addition to its known effect upon cytochrome oxidase, azide was found to inhibit the alternative pathway of Neurospora with half-maximal inhibition occurring at 1.3 mM azide. This finding indicates that the activities of at least some of the "novel" azide-sensitive oxidases that have been discovered recently in organisms with inducible or constitutive cyanide-insensitive respiratory systems might be attributable to the "standard" salicylhydroxamate-sensitive mitochondrial alternative pathway.