Effects of uncoupling of mitochondrial energy conservation on the ultradian clock-driven oscillations in Saccharomyces cerevisiae continuous culture.

Protonophores have several different perturbative effects on dissolved O2 concentrations in continuous cultures of Saccharomyces cerevisiae. As well as uncoupling energy conservation from mitochondrial electron transport in vivo, they reset ultradian clock-driven respiratory oscillations and produce cell cycle effects. Thus, additions at low concentration (1.25 microM) of either m-chlorocarbonyl-cyanide phenylhydrazone (CCCP) or 5-chloro-3-t-butyl-2-chloro-4(1)-nitrosalicylanilide (S13) led to phase resetting of the 48 min ultradian clock-driven respiratory oscillations. At 2.5 microM CCCP or 4 microM S13, transient inhibition of oscillatory respiration (for 5 h) preceded synchronisation of the cell division cycle seen as a slow (9 h period) wave that enveloped the 48 min oscillation. At still higher concentrations of CCCP (5 microM), the cell division cycle was prolonged by about 7 h, and during this phase, the respiratory oscillation became undetectable. The significance of these observations with respect to the time-keeping functions of the ultradian clock is discussed.