Respiratory inhibition by cyanide and salicylhydroxamic acid on the three species of Paramecium in stationary growth phase

1. 1. Paramecia in stationary growth phase consumed oxygen at a constant rate, exhibiting 21.5 nM/min/mg protein of the cells at 27°C. 2. 2. Respiratory inhibition by 1 mM KCN was significantly high in the following order: P. caudatum (96%) > P. multimicronucleatum (87%) > P. tetraurelia (77%). 3. 3. In the presence of cyanide (CN), 1 mM salicylhydroxamic acid (SHAM) suppressed a large part of the CN-insensitive respiration in the cells, and the cumulative inhibition by CN and SHAM reached approx. 95% in all of the Paramecium species examined. SHAM in the absence of CN caused no detectable change in the respiration of the cells. 4. 4. Oxygen affinity for the CN-sensitive respiration was far stronger than that for the CN-insensitive respiration in the whole cells of Paramecium.