Abstract
The cyanogenic low-temperature basidiomycete (Coprinus psychromorbidus Redhead and Traquair), unlike other cyanide-tolerant fungi, does not detoxify cyanide via formamide hydro-lyase. Instead, tolerance apparently depends on cyanide-insensitive respiration involving activity of the mitochondrial alternative oxidase. Respiration and growth of young mycelium that lacks alternative oxidase activity are blocked both by cyanide and 1 mum antimycin. When activity of the alternative oxidase is elicited in young mycelium by 0.05 mm cyanide, subsequent treatment with antimycin stimulates respiration and fails to halt growth. Older mycelium becomes tolerant coincidentally with the release of cyanide by the mycelium. Tolerant older mycelium in medium containing 0.05 to 1.0 mum antimycin grows at 30 to 45% of the control rate. Cyanide- and antimycin-tolerant growth and respiration are blocked by salicyl hydroxamic acid, an inhibitor of the alternative oxidase, and by rotenone, which inhibits ATP synthesis at site I.