Abstract
Previous studies have shown that channel formation in the cytoplasmic membrane of Escherichia coli by colicin A and phage T5 leads to an efflux of cytoplasmic potassium and to a membrane depolarization. Here we show that upon opening of these channels, the intracellular ATP concentration is decreased to 10% of its original value in < 5 min. ATP is not found in the external medium, but is hydrolyzed in the cytoplasm into ADP and AMP. The rate of ATP hydrolysis depends on the number of channels and on their activity. ATP hydrolysis takes place if the F1F0-ATPase is absent or inhibited. Depolarization of the inner membrane is not the main cause of ATP hydrolysis. Opening of the phage and colicin channels also leads to an efflux of inorganic phosphate. Conditions that prevent the efflux of phosphate (i.e. depolarization of the cells and high external phosphate concentration) prevent ATP hydrolysis. We propose that ATP is hydrolyzed as a consequence of a shift in the ATP equilibrium due to the efflux of phosphate through the channels. The consequences for the cells of this ATP depletion are discussed.
Highlights
Previousstudies have shown that channel formation a decrease in the electrochemical gradient of protons
We proposethatATP is hydrolyzed as a periments showing that colicin K-induced ATP hydrolysis is consequence of a shift in the ATP equilibrium due to prevented in a strain mutated in the uncA gene
We show that the loss of ATP following channel formation by colicins and phage T5 corresponds to its hydrolysis into ADP and AMP
Summary
ColicinA Induces Decrease in IntracellularATP Concentration That Is Correlatedto ChannelActivity-The ATP content of E. coli cells fell to 10% of its initial value within 4 min following addition of colicin A (Fig. la). Increasing phage multiplicity increased the rate of potassium efflux and of ATP decrease with similar patterns (Fig. 6b). This suggests that the decrease in ATP is correlated tothe opening of the channel. On the other hand, increasing the concentration of external phosphate resulted in a decrease in the rate of ATP hydrolysis (Fig. 7). When the external Piconcentration was raised above 30 mM (ix. a concentration equal to inthternal one), ATP hydrolysis was not observed anymore
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