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Phosphoketolase
Pathway -
Some
bacteria
such
as
the
heterolactic
bacteria
(Leuconostoc
mesentroides)
degrade
glucose
producing
lactic
acid
in
addition
to
acetate,
ethanol
and
CO2.
The
overall
reaction
is:
Glucose --> Lactic
acid
+
Ethanol
+CO2
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In
this
pathway,
hexose
is
first
decarboxylated
to
a
pentose
which
then
undergoes
fission.
Important
enzymes,
involved
are
glucose-6-phosphate
dehydrogenase
and
6-phosphogluconate
dehydrogenase.
The
net
yield
of
ATP
generated
by
this
pathway
when
glucose
is
the
substrate
is
one,
while
when
a
pentose
is
the
substrate,
2
moles
of
ATP
are
produced.
This
is
because
of
the
loss
of
the
high
energy
bond
of
the
acetyl
phosphate
by
the
reduction
to
ethanol.
Thus,
ethanol
production
by
any
route
other
than
the
pyruvate
decarboxylation
and
acetaldehyde
reduction
is
energetically
wasteful
to
the
organisms.
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