Regulation of glycolysis of Lactococcus lactis ssp. cremoris MG 1363 at acidic culture conditions

Publisher Summary This chapter discusses the regulation of glycolysis of Lactococcus lactis ssp. cremoris MG 1363 at acidic culture conditions. To study the effect of the pH of the medium on the regulation of the central metabolism of L . lactis MG 1363, the concentration of glycolytic intermediates and coenzymes and the specific activities of some enzymes are measured in cell-flee extracts prepared from cells growing exponentially in the different pH-regulated cultures. Among the crucial enzymes shown to be important in the control of glycolysis in L. lactis. To take into account the effect of the intracellular environment on the enzyme activities, the internal pH of L. lactis cells growing exponentially at different pH conditions is measured by determining the internal to external gradient of 14 C-benzoic acid after centrifugation of the cells through silicone oil. The change in pH value between the cytoplasm and the culture medium increased with the medium acidity, from 0.7 at pH 6.6 to 1.2 at pH 4.4. The glyceraldehyde-3-phosphate dehydrogenase is strongly inhibited by decreased pH values. The residual activity taking into account the internal pH value of the bacterium decreased from 86 to 7% of the maximal value when the pH of the medium fell from 6.6 to 4.4. On the other hand, lactate dehydrogenase activity is not affected by the pH values in the range tested (from 5.6 to 7.8).