N. Asanuma et T. Hino, Effects of pH and energy supply on activity and amount of pyruvate formate-lyase in Streptococcus bovis, APPL ENVIR, 66(9), 2000, pp. 3773-3777
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.