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||"Assuming the presence of about 1,000 different metabolites in cells gives, for the average intracellular metabolite concentration Xj, a value of about 10^-3 mol/L. Of course, there will be a wide distribution of concentrations, so [investigators] can expect an intracellular concentration range of 10^-2 to 10^-4 mol/L, which is equivalent to 20–0.20 µmol/g dry biomass. These values are indeed found as shown in Table 1." "Another general aspect of metabolites is a fast, order of seconds, turnover time (t.o.t.) of each metabolite. The t.o.t. of a metabolite Xj is defined as (t.o.t.) Xj=Xj/Vsum, with Xj the metabolite concentration and Vsum the sum of all production rates of this metabolite. Because Xj is low and Vsum can be high, one indeed finds t.o.t. of the order of seconds (Table 1)."