Fig. 2. (A) Mass action ratio vs glycolytic flux rate (i.e. net forward flux at the phosphoglucoisomerase reaction). The Haldane relationship predicts that extremely small variation in the mass action ratio is enough to account for the range of glycolytic flux rates of 4.64-13.0 µmol g^-1 min^-1 observed across species. (B) Glycolytic flux rate (i.e. net forward flux at the PGI reaction) vs glucose 6-phosphate concentration. Holding fructose 6-phosphate concentration at 0.1 mmol l^-1, the Haldane relationship predicts that the range of glycolytic flux rates of 4.64-13.0 µmol g^-1 min^-1 observed across species is achieved by a change in glucose 6-phosphate concentration of about 0.02 mmol l^-1.