Download Pyruvate Dehydrogenase Complex and Tricarboxylic Acid

Pyruvate Dehydrogenase
Complex
and
Tricarboxylic Acid-cycle
May 12, 2014
Hagop Atamian
[email protected]
Recall from Glycolysis
• Glycolysis is the first step of aerobic cellular
respiration.
• The end product of glycolysis is pyruvate .
• Glycolysis takes place in the cytosol
where all the enzymes are present.
of cells
• Pyruvate enters the mitochondrion to be metabolized
further.
Mitochondrial Compartments
Pyruvate Dehydrogenase Complex
• Pyruvate dehydrogenase is a large complex containing
many copies of each of three enzymes:
– Pyruvate Dehydrogenase (PDH)
– Dihydrolipoyl Transacetylase (DALT)
– Dihydrolipoyl Dehydrogenase (DLD)
• Has five cofactors:
– TPP
Catalytic
– Lipoic acid
– FAD
– NAD+
– CoA-SH
Oxidative Decarboxylation of Pyruvate
O
CH3
C
NADH + H+
NAD+
CO2
O
C
O-
Pyruvate
dehydrogenase
complex
O
Pyruvate
CH3
C
S
CoA
Acetyl CoA
CoA-SH
Decarboxylation
O
CH3
C
O
2e-­‐
-­‐
Oxidation
CH3
C
+
Oxidative Decarboxylation of Pyruvate
Pyruvate Dehydrogenase Complex
• Pyruvate dehydrogenase is a large complex containing
many copies of each of three enzymes:
– Pyruvate Dehydrogenase (PDH)
– Dihydrolipoyl Transacetylase (DALT)
– Dihydrolipoyl Dehydrogenase (DLD)
• Has five cofactors:
– TPP
Catalytic
– Lipoic acid
– FAD
– NAD+
– CoA-SH
What is the Net Result of PDHc Reactions?
Pyruvate + CoA + NAD+——> CO2 + acetyl-CoA + NADH + H+
Acetyl CoA: A Common Meeting Point
• Acetyl-CoA is an important molecule in metabolism.
• In chemical structure, acetyl-CoA is the thioester
between coenzyme A (a thiol) and acetic acid (an acyl
group carrier).
O
CH3
C
S
CoA
• Several metabolic pathways converge to Acetyl-CoA
including:
1. Fatty acid metabolism
2. Amino acid metabolism
3. Carbohydrate metabolism
Acetyl CoA: A Common Meeting Point
synthesis of the
neurotransmitter
acetylcholine
Tricarboxylic Acid Cycle (TCA-cycle)
• Also known as citric acid cycle and Krebs cycle.
Hans Adolf Krebs
(1900-­‐1981)
Nobel Prize in Medicine (1953), which he
shared with Fritz Lipmann.
h$p://en.wikipedia.org/wiki/Hans_Adolf_Krebs
TCA-cycle
• Harvests chemical energy from biological fuel in the
form of electrons in NADH and FADH2.
• Consists of a series of eight reactions.
• Converts acetyl-CoA to two CO2 while conserving the
free energy for ATP production.
– The energy is stored as: three NADHs, one
FADH2, and one GTP.
• Intermediates from the TCA-cycle can be used to
synthesize molecules such as amino acids and fatty
acids.
Summary
• The final product of glycolysis is pyruvate. It is located
in the cytosol .
• In order to enter the TCA-cycle pyruvate has to be
oxidized to Acetyl-CoA,
converted
acetyl-CoA releasing C02.
pyruvatedehydrogenase
dehydrogenase complex
• This is achieved by pyruvate
complex
(PDHc)
(PDHc), which consists of three
three enzymes and is located
in the mitochondrial
matrix.
mitochondrial matrix
• use inner mitochondrial membrane is impermeable.
Summary
• The primary function of the TCA-cycle is oxidation of
acetyl
CoA to two CO2.
acetyl CoA
• The energy from these oxidation reactions is
captured as:
1. NADH
NADH
2. FADH2
FADH2
• e.
TCA-cycle in Detail
Total of eight
reactions
Reaction 1: Condensation Reaction
CoA-SH
O
CH3
C
S
CoA
+
O-
Acetyl CoA
O
O
C
1
C
2
*
O
CH2
3
C
4
O-
Oxaloacetate
Citrate
Synthase
H 2O
Citrate
O-
O
O
O-
C
CH2
C1
C
*
OH
O
CH2
3
C
4
O∆G°’ = -­‐32.2 kJ/mol
Reaction 2: Rearrangement Reaction
O-
O
O
O-
C
CH2
C1
C
*
O
CH2
3
O-
C
4
Citrate
OH
Aconitas
e
O-
O
C
O
O-
C1
OH
O
CH2
CH
*
CH
3
C
4
O-
Isocitrate
∆G°’ = 13.3 kJ/mol
Reaction 3: First Oxidative decarboxylation
CO2
O
C
NAD+
O
O-
OC1
OH
O
CH2
CH
2
CH
3
C
4
O-
Isocitrate
dehydrogenase
O
O-
C
CH2
CH2
2
O
O
C
3
C
4
O-
NADH + H+
Isocitrate
The only irreversible
reaction.
α-ketaglutarate
∆G°’ = -­‐20.9 kJ/mol
Reaction 4: Second Oxidative Decarboxylation
CO2
O
O-
C
CH2
CH2
2
O
O
C
3
C
4
O-
α-ketaglutarate
Back to four
carbon molecule
α-ketaglutarate
dehydrogenase
NAD+
NADH + H+
∆G°’ = -­‐33.5 kJ/mol O
O-
C
O
CH2
CH2
2
C
3
S
CoA
Succinyl CoA
Reaction 5: Oxidation Reaction
O
O-
C
CoA-SH
O
CH2
CH2
2
C
3
S
CoA
Succinyl CoA
Succinyl CoA
synthetase
GDP
O
O-
C
GTP
O
CH2
CH2
2
C
3
O-
Succinate
∆G°’ = -­‐2.9 kJ/mol Summary
• In terms of carbons:
A two carbon acetyl group has been linked to
oxaloacetate and two CO2 molecules have been
liberated.
• In terms of energy captured:
Two NAD+ have been reduced to NADH + H+.
One ATP produced.
Leaving us with a molecule of succinate
Reaction 6: Oxidation Reaction
O
O-
C
Alkane
CH2
CH2
2
O
C
3
O-
Succinate
Dehydrogenase
(membrane bound)
O
O-
C
Alkene
CH
CH
2
Succinate
FAD
FADH2
O
C
3
O-
Fumarate
∆G°’ = 0 kJ/mol Reaction 7: Hydration Reaction
O
O-
C
O
CH
H2O
O-
CH
2
C
3
O-
Fumarate
Fumarase
O
OH
C
CH
H
O
CH
2
C
3
Malate
O∆G°’ = -­‐3.8 kJ/mol
Reaction 8: Final Oxidation Reaction
Regeneration of Oxaloacetate
O-
O
OH
C
CH
H
O
CH
2
C
3
Malate
O-
Malate
dehydrogenase
NAD+
O-
O
O
H
C
C
CH
2
O
C
3
O-
NADH + H+
Oxaloacetate
∆G°’ = 29.7 kJ/mol Regenerated VS Starting Oxaloacetate
O-
O-
O
O
H
C
C
CH
2
O
O
C
1
C
2
O
O-
C
3
Oxaloacetate
O
CH2
3
C
4
O-
Oxaloacetate
Review of the TCA-cycle
Acetyl CoA
Citrate Synthase
NADH
Malate
dehydrogenase
OAA
Citrate
Aconitase
Malate
Isocitrate
Fumarase
Isocitrate
dehydrogenase
NADH & CO2
Fumarate
FA
Succinate
DH
dehydrogenase
2
α-Ketaglutarate
α-Ketaglutarate
dehydrogenase
GTP Succinyl
Succinate
CoA
NADH & CO2
Succinyl CoA
syhthetase
h$p://tru-­‐wealth.blogspot.com/2013/05/your-­‐bodys-­‐chemistry-­‐pyruvate-­‐for.html
TCA-cycle: In Terms of Carbon # of the
Different Steps
h$p://www.uic.edu/classes/bios/bios100/summer2002/lect10.htm
What’s Next
• We saw how the acetyl-CoA made from glucose, fat,
or protein burnt and energy captured as NADH and
FADH2.
• Next lecture we will see how this captured energy is
used to make ATP via oxidative phosphorylation.
THE END
More questions??
Please email me @
[email protected]