Intracellular concentrations of ATP, ADP and AMP in cell extracts derived from a pH-controlled continuous culture. Two samples were quenched, one with 60% MeOH and 70 mM HEPES (pH 5.5) and the other 60% MeOH and 0.85% ammonium carbonate (pH 5.5). The two cell pellets were washed with the same quenching solution, extracted with cold methanol and freeze-dried. Finally, ATP, ADP and AMP were quantified. The coefficient of variance of this quantification method was less than 7%. The intracellular concentrations were determined using the intracellular volume of E. coli (2.15 mL g-1 dry weight) .
The energy charge (EC) of the cell extract was calculated by