Download How does pyruvate enter mitochondrion? Enzymes in PDH bind

How does pyruvate enter
mitochondrion?
Glycolysis
glu
glu
g-6-P
||
f-6-P
f-1,6-bisP
gly.P
gly.P
3-PG DHAP
DHAP
PEP
pyr
- pyruvate moves easily through the
permeable outer membrane but
must be transported through the
inner mitochondrial membrane by a
protein carrier molecule
lactate
pyr
Enzymes in PDH bind:
• Thiamin pyrophosphate (TPP)
• Lipoic acid
• CoEnzyme A (CoA)
Oxidation of pyruvate
Main function: formation of
acetyl CoA
Location in cell: mitochondrial
matrix
• Flavin Adenine Dinucleotide (FAD)
• Nicotinamide Adenine Di. (NAD)
Oxidation of pyruvate
Endproduct: acetyl CoA; e for ETS
O
||
CH3-C ~S - CoA
Regulation:
ATP, NAD:H and
acetyl CoA allosterically
inhibit PDH
PDH
Substrate: pyruvate CH 3
C=0
- O-C = O
Pyruvate
acetyl CoA
is a one-way street
- in the mitochondrial matrix, PDH
oxidizes pyruvate to acetyl
in a series of reactions which
are IRREVERSIBLE in the cell
Oxidation of pyruvate
Oxidation of pyruvate
Pyruvate Dehydrogenase, PDH,
catalyzes the conversion
of pyruvate to acetyl
All the enzymes in this short path
are associated into a large
complex in matrix of
mitochondria
step 1: acetaldehyde
formation
CH3 - C - C - O
|| ||
O O
~
PDH N
PDH N TPP
S
size relationships
C=O
|
O
-
PDH complex is composed of 72
subunits; 6 different kinds of
polypeptides
- 5 different catalytic functions;
- some subunits are
regulatory
active site
pyruvate
catalytic
subunit of
PDH
S
CH3 - C = O
step 2: transfer 2 C
fragment to lipoic acid on
DHLT
step 3: transfer to CoA
HS - CoA
TPP PDH
TPP
Thiamin pyro
phosphate (TPP)
PDH
||
S
HS
CH3 - C = O
~
~
CH3 - C - OH
S
CH3 - C = O
HS
S
S
O
||
CH3 - C ~S - CoA
acetyl CoA
HS SH
DHLT
DHLT
subunit
lipoic
acid
DHLT
DHLT
size relationships
Coenzyme A
Step 4. Oxidation of dihydrolipoic acid
HS
SH
S
DHLT
DHLT
acetyl
catalytic
subunit of
Pyruvate
DHase
Step 5. Oxidation of FADH2
FAD.H2
FAD
NAD+
NAD:H
+ H+
S
DHLT
FAD
FAD.H.H
fate of acetyl
• Endproduct of pyruvate
oxidation is acetyl which enters
Tri-carboxylic acid cycle in
mitochondria
NAD:H donates hydride ion, H:
to Electron Transport System
TCA cycle
• Main function in metabolism
– aerobic production of energy
– TCA cycle intermediates act
as substrates for other
pathways
TCA cycle
Location of pathway in the cell
- enzymes of TCA cycle are
tightly bound to inner
mitochondrial membrane
- all cells with mitochondria
have TCA cycle
TCA cycle
Regulation of TCA cycle
O
||
CH 3 - C ~ S - CoA
acetyl CoA
Endproduct: - electrons for ETS in
H: ions and H atoms
- CO2
b. isocitrate dehydrogenase
ATP and NAD:H inhibit activity
ADP and NAD+ stimulate
aconitase
Citrate synthase
O
||
CH3 - C ~ S - CoA
acetyl CoA
O
O= C - C = O
|
H - C -H
|
O=C-O
oxaloacetate
HS - CoA
O = C - O|
H - C- H
| OHO -C - C = O
|
H-C-H
|
O = C - O-
citrate
O=C-O
|
H - C- H
| O
HO -C - C = O
|
H - C -H
|
O=C-O
citrate
isocitrate
ketoglutarate DHase
isocitrate DHase
O=C-O
O=C-O
|
|
O
H - C- H
C = O H - C- H
| O
|
H- C -H
H: C - C = O
|
|
NAD+
O =C
HO -C - H
NAD:H
|
|
+ H+ O = C - O
O=C-O
isocitrate
Fe++
O=C-O
|
H - C- H
| O
H- C - C = O
|
HO -C -H
|
O=C-O
- KG
O=C-O
|
H - C- H
|
H- C -H
|
O =C
|
O=C-O
- KG
O=C=O
HS - CoA
O=C-O
|
H - C- H
|
H- C -H
|
O =C
~
Substrate:
a. citrate synthase
catalyzes rate-limiting step
-inhibited by ATP and NAD:H
NAD+
NAD:H
S - CoA
succinyl CoA
ketoglutarate DHase
complex
-KG DHase is virtually identical
to pyruvate DHase (PDH)
- 72 subunits;
- 6 different types of polypeptides
O=C-O
CoA-SH
|
H - C- H
|
H- C -H
|
G-r-P~P
O =C
+ Pi
GTP
S - CoA
succinyl CoA
~
ATP, NAD:H and succinyl CoA
are strong allosteric inhibitors
succinyl thiokinase
succinate DHase
O=C-O
|
H-C:H
:
H: C - H
|
O =C-O
O=C-O
|
H-C
::
C-H
|
FAD FAD.H.H
O =C-O
succinate
O=C - O
|
H-C- H
|
H-C- H
|
O= C - O
succinate
fumarase
O=C-O
|
H :O:H
H-C
::
O=C-O
|
.
H - C . OH
:
C-H
|
O =C-O
.
H.C-H
|
O =C-O
fumarate
malate
fumarate
glycogen
malate DHase
O=C-O
|
H : C : O:H
|
H - C - H NAD+
|
O =C-O
NAD:H
malate
+ H+
O=C-O
|
C=O
|
H-C-H
|
O=C-O
oxaloacetate
OAA
glu
glu
g-6-P
f-6-P
gly.P
f-1,6-diP
OAA
malate
malate
DHAP
3-PG DHAP gly.P
PEP pyr pyr
acetyl Co A
OAA
citrate
pyr malate
isocitrate
OAA
succinate
G
succ.CoA