Control analysis of the importance of phosphoglycerate enolase for metabolic fluxes in Lactococcus lactis subsp. lactis IL1403

The glycolytic enzyme phosphoglycerate enolase (PGE) catalyses the step from 2-phosphoglycerate to phosphoenolpyruvate in glycolysis. A control analysis of PGE on growth, glycolytic flux and product formation in Lactococcus lactis subsp. lactis IL1403 is presented. A library of strains with a modulated expression of PGE from 36 to 232% relative to wildtype level was constructed. Selected strains were studied with respect to growth, glycolytic flux and product formation in a chemically defined medium. On the basis of these data, flux control coefficients of PGE on the respective fluxes were calculated. At wildtype level, PGE was found to have no significant flux control on growth, glycolytic flux or product formation, but at 36% of PGE activity relative to wildtype, the flux control on the growth rate was estimated to be C(PGE)J(micro) approximately equal to 0.7, on the glycolytic flux C(PGE)J(g) approximately equal to 0.8, on lactate formation C(PGE)J(lactate) approximately equal to 1.3, on formate formation C(PGE)J(formate) approximately equal to 0.5 and on acetate formation C(PGE) J(acetate) approximately equal to 0.25. These flux control coefficients show that the metabolism of L. lactis subsp. lactis IL1403 becomes slightly more mixed acid at reduced PGE activities. Estimation of the relative turnover of PGE indicates that excess capacity of PGE in L. lactis IL1403 may be as low as twofold.