Acquisition and Loss of Rotenone Sensitivity in Torulopsis utilis

Torulopsis utilis yeast cells growing exponentially on synthetic medium with ethanol as carbon and energy source are insensitive to rotenone; the cells acquire the rotenone‐sensitive component of the mitochondrial electron transport chain upon entering an ethanol‐depleted stationary phase. The rotenone‐sensitive site is lost when growth is restimulated with ethanol, but not when growth is restimulated with glycerol or acetic acid. Growth limitation by iron or by glucose or glycerol is also characterized by acquisition of the rotenone‐sensitive site, upon entering stationary phase. The transition from rotenone‐sensitive to ‐insensitive can also be studied by the use of semi‐continuous culture in a chemostat. Studies with the protein synthesis inhibitors cycloheximide and chloramphenicol indicate that protein synthesis on cytoplasmic ribosomes is required both for the acquisition and the loss of the rotenone‐sensitive site. The acquisition of rotenone sensitivity is apparently associated with an increased phosphorylation efficiency, as evidenced by measurements of P/O ratios.