In silico model for the interplay of glycolysis and the pentose phosphate pathway in response to GAPDH or TPI inactivation. (a) Predicted changes of the cytoplasmic NADPH/NADP+ ratio of the unfitted model. The NADPH/NADP+ ratio increases in correlation with the rate of TPI (blue) or GAPDH (red) inactivation. (b) Quantitative accuracy of the metabolic model before and after parameter fitting. Upper panel, 21 measured metabolite concentrations (seven metabolites under three conditions) are plotted against the predicted values before fitting. Lower panel, data versus prediction after parameter fitting. (c) As (a), but after parameter fitting. (d) Comparison of quantitative predictions made with the parameter-fitted and the measured metabolite concentrations. Changes relative to the wild-type strain values are shown. Black and red bars correspond to yeast cells with inactivated GAPDH, green and yellow bars correspond to reduced TPI activity.