Schematic representation of a simplified model of glycolysis and the trehalose cycle in the yeast Saccharomyces cerevisiae (adapted from). X
represent dependent variables and fluxes, respectively. One inhibitory interaction is shown in red. Abbreviations: X1, extracellular glucose; X2, intracellular glucose; X3, glucose 6-phosphate; X4, trehalose; X5, fructose 1,6-bisphosphate; X6, extracellularly accumulating end products (ethanol, glycerol and acetate); X7, mass diverted into the pentose phosphate pathway; X8, mass consumed by other pathways (e.g., TCA); v1, glucose transport; v2, hexokinase and glucokinase; v3: aggregated step of all enzymatic steps between glucose 6-phosphate and the production of trehalose; v4, trehalase; v5, phosphoglucose isomerase and phosphofructokinase; v6, aggregated step of all enzymatic steps between fructose 1,6-bisphosphate aldolase and the release of end-products; v7, flux into the pentose phosphate pathway; v8, flux towards other pathways (leakage). Metabolites without available experimental measurements are shown in gray. The flux v6 (blue) is directly measurable from the time series of X6. Fluxes v3 and v4 (green) were estimated using the proposed method.