Biomedical Engineering Reference
In-Depth Information
Conversion of Pyruvate to Acetyl CoA
Pyruvate moves into the mitochondria by diffusion. Once inside the mitochondria, an
enzyme catalyzed reaction occurs that converts pyruvate (PV) into acetyl coenzyme A
(AC) as follows:
B
0
PV
þ
CoA
SH
!
PVCoA
ð
8
:
102
Þ
K
0
PVCoA
þ
NAD
þ
!
AC
þ
CoA
SH
þ
CO
2
þ
NADH
þ
H
þ
ð
Þ
q
PV
¼
J
PV
B
q
PV
q
CoA
0
q
CoA
¼
B
q
PV
q
CoA
þ
K
q
PVCoA
q
NAD
þ
0
0
q
PVCoA
¼
B
q
PV
q
CoA
K
q
PVCoA
q
NAD
þ
0
0
q
AC
¼
K
0
q
PVCoA
q
NAD
þ
where CoA-SH (CoA) is coenzyme A,
PVCoA
is the complex pyruvate dehydrogenase, and
J
PV
is the production of pyruvate given by Eq. (8.98). Keep in mind that from one glucose
molecule, two pyruvate molecules are created that pass into the mitochondria. Also note
that 2
NADH
þ
H
þ
FADH
2
to transfer acetyl coenzyme A across the
mitochondrial membrane, thus costing 2 ATP.
ð
Þ
are converted into 2
8.5.2 Krebs Cycle
The Krebs cycle involves a series of enzyme catalyzed reactions that reduce the acetyl
portion of acetyl coenzyme A in the mitochondrial matrix, as shown in Figure 8.25. The
Krebs cycle continuously recycles, reusing the substrates and enzymes with an overall reac-
tion given by
NAD
þ
þ
FAD
þ
Acetyl
-
CoA
þ
3
2
H
O
þ
ADP
þ
P
!
2
ð
8
:
103
Þ
NADH
þ
H
þ
CoA
SH
þ
2
CO
þ
FADH
þ
ATP
þ
3
ð
Þ
2
2
The reaction begins with the joining of
acetyl-coenzyme A
with
oxaloacetate
and water to form
citrate and is given by
B
1
K
1
AC
þ
H
2
O
þ
CS
þ
O
!
ACOCS
!
CT
þ
CoA
SH
þ
CS
ð
8
:
104
Þ
q
AC
¼
B
1
q
AC
q
H
2
O
q
CS
q
O
þ
J
AC
q
ACOCS
¼
B
q
AC
q
H
2
O
q
CS
q
O
K
q
ACOCS
1
1
where
acetyl coenzyme A based on Eq. (8.102).
The next step involves the reaction of
J
AC
is the flow
of
citrate
with the enzyme
aconitase
to create
isocitrate
,
which is given by
ð
8
:
105
Þ
