Adenosine Triphosphatase Activity and its Sensitivity to Ruthenium Red Oscillate during the Cell Cycle of Escherichia coli K12

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Abstract
A procedure was developed for the large-scale fractionation into size and age classes of bacteria from exponentially growing cultures of E. coli K12 by centrifugation through an equivolumetric gradient of sucrose in a zonal rotor. The resolution attained is superior to that in methods of this type described previously. The activity of ATPase was assayed in extracts from bacteria separated into size classes by this method and from synchronous cultures prepared by size selection. Activity approximately doubled during a cell cycle but the experiment data did not fit models of continuously or exponentially increasing activity during the cycle. ATPase activity may oscillate during the cell cycle with maxima at about 0.37 and 0.80 of a cycle. The fluctuations in activity greatly exceed the variations due to experimental error and, in the case of synchronous cultures, do not arise from perturbations in growth behavior following zonal gradient selection. Sensitivity of ATPase activity to 75 .mu.M-ruthenium red also fluctuates during the cell cycle, with maximum inhibition (60-80%) occurring near the middle of the rock, a time that does not coincide with maximum enzyme activity.

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