The Appearance and Characterization of Cyanide‐Resistant Respiration in the Fungus Candida albicans

Abstract

The respiration of yeast‐form cells of the dimorphic fungus Candida albicans became resistant to cyanide during aging treatment in the resting state. An alternative, cyanide‐resistant respiratory pathway was found to develop fully in cells aged at a concentration of 0.75 × 10⁹/ml or more at 25 C, but did not appear at 5 C. Chloramphenicol did not prevent the appearance of the alternative respiratory pathway. The effects of inhibitors, salicylhydroxamic acid (SHAM) and disulfiram (tetraethylthiuram disulfide), on respiration of aged cells were examined, and results indicated that SHAM binds at a site on the alternative respiratory pathway whereas disulfiram binds at two sites, one on the conventional respiratory pathway and the other on the alternative pathway. Thus, SHAM is a more selective inhibitor of the alternative respiration of C. albicans cells. SHAM‐titration of the alternative respiration revealed that less than 10% of the maximal activity of the alternative respiratory pathway was utilized under normal conditions, indicating that the alternative respiratory pathway makes a small contribution to the total respiration. It was therefore concluded that the alternative, cyanide‐resistant respiratory pathway operates fully when the cyanide‐sensitive, cytochrome pathway is blocked although aged cells possess both respiratory pathways.