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J. Bacteriol., May 1995, 2751-2759, Vol 177, No. 10
T Thevenot, D Brochu, C Vadeboncoeur and IR Hamilton
Sugar transport via the phosphoenolpyruvate (PEP) phosphotransferase system
involves PEP-dependent phosphorylation of the general phosphotransferase
system protein, HPr, at histidine 15. However, gram- positive bacteria can
also carry out ATP-dependent phosphorylation of HPr at serine 46 by means
of (Ser)HPr kinase. In this study, we demonstrate that (Ser)HPr kinase in
crude preparations of Streptococcus mutans Ingbritt and Streptococcus
salivarius ATCC 25975 is membrane associated, with pH optima of 7.0 and
7.5, respectively. The latter organism possessed 7- to 27-fold-higher
activity than S. mutans NCTC 10449, GS-5, and Ingbritt strains. The enzyme
in S. salivarius was activated by fructose-1,6-bisphosphate (FBP) twofold
with 0.05 mM ATP, but this intermediate was slightly inhibitory with 1.0 mM
ATP at FBP concentrations up to 10 mM. Similar inhibition was observed with
the enzyme from S. mutans Ingbritt. A variety of other glycolytic
intermediates had no effect on kinase activity under these conditions. The
activity and regulation of (Ser)HPr kinase were assessed in vivo by
monitoring P-(Ser)-HPr formation in steady-state cells of S. mutans
Ingbritt grown in continuous culture with limiting glucose (10 and 50 mM)
and with excess glucose (100 and 200 mM). All four forms of HPr [free HPr,
P approximately (His)-HPr, P-(Ser)-HPr, and P approximately
(His)-P-(Ser)-HPr] could be detected in the cells; however, significant
differences in the intracellular levels of the forms were apparent during
growth at different glucose concentrations.(ABSTRACT TRUNCATED AT 250
WORDS)
Copyright © 1995, American Society for Microbiology
Regulation of ATP-dependent P-(Ser)-HPr formation in Streptococcus mutans and Streptococcus salivarius
Department of Oral Biology, University of Manitoba, Winnipeg, Canada.
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