The respiratory chain of Paramecium tetraurelia in wild type and the mutant Cl1. II. Cyanide-insensitive respiration. Function and regulation.

1. The cyanide-insensitive respiration in Paramecium tetraurelia was found to be located in mitochondria. 2. Sensitivity of the mitochondrial respiration to cyanide depended on growth conditions. Under standard conditions of growth, 15--20% of respiration was insensitive to 1 mM cyanide. Full resistance to 1 mM cyanide was observed by growing cells in the presence of erythromycin (100--400 microgram/ml) 0.2 mM cyanide. The mitochondrial respiration of the mutant Cl1 harvested during the exponential phase of growth was largely insensitive to cyanide (more than 80%). 3. Pyruvate was oxidized at the same rate by wild type mitochondria and mitochondria of the mutant Cl1. In contrast, succinate oxidation was 2--3 times faster in mitochondria of the mutant Cl1 than in wild type mitochondria. 4. The cyanide-insensitive respiration was inhibited by 1 mM salicylhydroxamic acid to nearly 100%. Other efficient respiratory inhibitors included amytal and heptylhydroxyquinoline. Antimycin was not inhibitory even at concentrations as high as 5 microgram/mg protein, a finding consistent with the lack of antimycin binding sites.