Uncoupling of grwoth and acid production in Streptococcus cremoris

In lactose and leucine-limited continuous cultures of Streptococcus cremoris a linear relationship exists between specific rate of lactate production and specific growth rate. The rate of acid production in leucine-limited cultures is much higher than in lactose-limited cultures, indicating that under these conditions metabolic energy production is not coupled to growth and that metabolic energy has to be dissipated S. cremoris contains phosphofructokinase and fructose-1,6-diphosphatase, joint action of these two enzymes results in an ATP consuming futile cycle. Analyses of intracellular metabolite pools suggested that AMP and phosphoenolpyruvate play important roles in the regulation of the activity of this futile cycle.Abbreviations PEP Phosphoenolpyruvate - PFK phosphofructokinase (EC 2.7.1.11) - FBPase fructose-1,6-bisphosphatase (EC 3.1.3.11)