Synchronous cultures of the soil amoeba , prepared by a size selection procedure involving minimum metabolic perturbation, divided with a high degree of synchrony and showed a discrete S-phase of DNA synthesis. Oxygen uptake rates doubled overall during one cell cycle time of 7 to 8 h but rose to seven distinct maxima during this period. Control experiments showed that the selection procedure did not give rise to the oscillations. The maxima of respiration were more sensitive to inhibition by cyanide than were the minima of respiration; the effect of carbonyl cyanide -trifluoro-methoxyphenylhydrazone (an uncoupler of oxidative phosphorylation) was, however, greater at respiratory minima, than at the maxima. Pool levels of ATP, ADP and AMP also oscillated during the cell cycle with maximum amplitudes (peak-trough, % minimal values) of 108, 194 and 520, respectively. Adenylate charge values varied between 0.63 and 0.88. Respiratory maxima were in phase with maximum ADP levels but out of phase with maxima of ATP/ADP ratios. These results suggest that the overall changes in respiration rates during the cell cycle of are the result of respiratory control.


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