METABOLIC CONTROL ANALYSIS OF GLYCOLYSIS IN TUBER TISSUE OF POTATO (SOLANUM-TUBEROSUM) - EXPLANATION FOR THE LOW CONTROL COEFFICIENT OF PHOSPHOFRUCTOKINASE OVER RESPIRATORY FLUX

We have applied Metabolic Control Analysis (MCA) in an attempt to dete rmine the distribution of glycolytic flux control between the steps of glycolysis in aged disks of potato tuber under aerobic conditions, us ing concentrations of glycolytic metabolites in tuber tissue from a ra nge of transgenic potato plants and published enzyme kinetic data. We modelled the substrate and effector kinetics of potato tuber phosphofr uctokinase (PFK) by reanalysing published results, Despite the scarcit y of reliable kinetic data, our results are in agreement with experime ntal findings namely that, under the conditions described, PFK has lit tle control over glycolytic flux. Furthermore our analysis predicts th at under these conditions far more control lies in the dephosphorylati on of phosphoenolpyruvate and/or in the steps beyond. We have validate d the results of our analysis in two ways. First, predictions based on calculated concentration control coefficients from the analysis show generally good agreement with observed metabolite deviation indices di scussed in the preceding paper [Thomas, Mooney, Burrell, and Fell (199 7) Biochem. J. 322, 111-117]. Second, sensitivity analysis of our resu lts shows that the calculated control coefficients are robust to error s in the elasticities used in the analysis, of which relatively few ne ed to be known accurately, Experimental and control analysis results a gree with previous predictions of MCA that strong co-operative feedbac k inhibition of enzymes serves to move flux control downstream of the inhibiting metabolite, We ( )conclude that MCA can successfully model the outcome of experiments in the genetic manipulation of enzyme amoun ts.