Effects of pH and energy supply on activity and amount of pyruvate formate-lyase in Streptococcus bovis

The enzyme system of pyruvate formate-lyase (PFL) in Streptococcus bovis wa s investigated by isolating PFL and PFL-activating enzyme (PFL-AE) from S, bovis, flavodoxin from Escherichia coli, and chloroplasts from spinach. In this study, the PFL and PFL-AE in S, bovis were found to be similar to thos e in E. coli, suggesting that the activating mechanisms are similar. The op timal pH of S, bovis PFL was 7,5, which is in contrast to the optimal pH of S, bovis lactate dehydrogenase, which is 5,5, The apparent ii, of S, bovis PFL was 2 mM, The intermediates of glycolysis, dihydroxyacetone phosphate (DHAP) and D-glyceraldehyde-3-phosphate (GAP), were shown to inhibit PFL ac tivity. The concentrations of intracellular DHAP and GAP in S, bovis ranged from 1.9 mM to less than 0.1 mM and from 0.6 mM to less than 0.05 mM, resp ectively, depending on the energy supply. The,vide variations in DHAP and G AP levels indicated that PFL activity is allosterically regulated by these triose phosphates in vivo, The amount of PFL protein, as determined by West ern blot analysis with polyclonal antibody, changed in parallel with the le vel of pfl-mRNA, responding to the culture conditions. These observations c onfirm that PFL synthesis is regulated at the transcriptional level and sup port the hypothesis that S, bovis shifts the fermentation pathway from acet ate, formate, and ethanol production to lactate production when the pH is l ow and when excess energy is supplied.