Download Pyruvate Dehydrogenase

Aerobic Metabolism
Summary of Anaerobic Glycolysis
Glucose + 2 ADP + 2 Pi
2 Lactate + 2 ATP + 2 H2O + 2 H+
Energetics of Fermentation
Glucose ——> 2 Lactate
∆Go’ = -200 kJ/mol
Glucose + 6 O2 ——> 6 CO2 + 6 H2O
∆Go’ = -2866 kJ/mol
Most of the energy of glucose is still
available following glycolysis!
Carbon Atom Oxidation
CH2 —> CH2OH —> C=O —> COOH —> CO2
Glucose
Lactate
Oxidative Fuel Metabolism
Figure 17-1
Oxidation-Reduction Reactions:
Electron Transfer
Substrate —> NAD+ or FAD —> Electron Carriers —> O2
Electron Transport
Oxidative Phosphorylation
Citric Acid Cycle
Figure 17-2
Electron Transport
Oxidative Phosphorylation
Substrate·H2
(reduced)
Substrate
(oxidized)
Acceptor
(NAD+ or FAD)
Reduced e– carrier
Etc.
Acceptor·H2
(NADH or FADH2)
Oxidized
e–
carrier
Electron Transport
[Proton Pumping]
Oxidative Phosphorylation
ADP + Pi
ATP
2 e–
H2O
2 H+ + 1/2 O2
Electron Transport
Oxidative Phosphorylation
Summary of Citric Acid Cycle
Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi
2 CO2 + 3 NADH + 3H+ + FADH2 + GTP + CoA-SH
Pyruvate Dehydrogenase:
Synthesis of Acetyl-CoA
Thioester
Acetyl-CoA
Sources of Acetyl-CoA
• Carbohydrates (sugars via glycolysis)
• Fats (fatty acids)
• Proteins (amino acids)
Pyruvate Dehydrogenase
(Formation of Acetyl-SCoA)
NAD+
NADH + H+
O
CH3
C
O
COOH
Pyruvate
+ CoenzymeA
SH
CH3
C
S
CoA + CO2
Acetyl–SCoA
Oxidative Decarboxylation
Pyruvate Dehydrogenase
(Multienzyme Complex)
• E1: Pyruvate Dehydrogenase or
Pyruvate Decarboxylase
• E2: Dihydrolipoyl Transacetylase
• E3: Dihydrolipoyl Dehydrogenase
Multienzyme Complexes
• Enhanced reaction rates
• Channeling of reaction intermediates
• Coordinate regulation
Electron Micrograph of E. coli
Pyruvate Dehydrogenase
Figure 17-3a
Organization of E. coli
Pyruvate Dehydrogenase Complex
Pyruvate Dehydrogenase
(Mammalian Enzyme)
• E1, E2, and E3
• E3 binding protein
• Kinase (regulation)
• Phosphatase (regulation)
Coenzymes and Prosthetic Groups
of Pyruvate Dehydrogenase
Table 17-1
Thiamin Pyrophosphate
O
CH3
CH2 CH2 O P
NH2
CH2 N
N
CH3
N
S
O–
O
O
P
O–
O–
Thiamin Pyrophosphate
O
CH3
CH2 CH2 O P
NH2
CH2 N
N
CH3
N
S
O–
O
O
P
O–
O–
Lipoic Acid
HOOC
(CH2)4
S
S
Reduction of Lipoamide
E2
E2
Figure 17-7
Coenzyme A
O
HS
CH2
CH2
NH
C
O
CH2
CH2
NH
C
CH3
CH
C
OH
CH3
CH2
Pantothenic Acid (vitamin B5)
OADP( 3'P)
NAD+
O
C
O
P O CH2
O–
O
N
O
OH
O
P O CH2
O–
OH
NH2
Nucleotide
OH
O
A
OH
Nucleotide
Flavin Adenine Dinucleotide (FAD)
Figure 14-12
Reduction of FAD
H
O
H3C
2 H·
N
H3C
O
N
NH
NH
H3C
FAD
N
N
CH2
CH2
H
CHOH
CHOH
N
N
CHOH
O
H3C
FADH2
CHOH
CHOH
CHOH
CH2OADP
CH2OADP
O
Pyruvate Dehydrogenase
(Formation of Acetyl-SCoA)
NAD+
NADH + H+
O
CH3
C
O
COOH
Pyruvate
+ CoenzymeA
SH
CH3
C
S
CoA + CO2
Acetyl–SCoA
Oxidative Decarboxylation
Overall Reaction of
Pyruvate Dehydrogenase
Reaction order of Pyruvate Dehydrogenase
Mechanism of Pyruvate Dehydrogenase
(Decarboxylation of Pyruvate)
CO2
E1–TPP
O
+
E1–TPP
H3C C OH
H3C C COOH
Pyruvate
E1–TPP
H3C C OH
C
O
O–
Same mechanism as Pyruvate Decarboxylase
Mechanism of Decarboxylation of Pyruvate
Page 572
Remainder
of Reaction
Reaction order of Pyruvate Dehydrogenase
Mechanism of Pyruvate Dehydrogenase
(Hydroxyethyl Group Transfer)
E1–TPP
+
H3C
C
OH
H+
E2
S
E2
S
H3C
S
SH
C
O
+ E1–TPP
Forms of Lipoamide
Mechanism of Hydroxyethyl Group Transfer
Page 574
Reaction order of Pyruvate Dehydrogenase
Mechanism of Pyruvate Dehydrogenase
(Transesterification)
E2
S
C
H3C
SH
O
+
CoA–SH
E2
+
SH SH
O
H3C
C
SCoA
Mechanism of Transesterification
Page 574
Reaction order of Pyruvate Dehydrogenase
Mechanism of Pyruvate Dehydrogenase
(Reoxidation of Dihydrolipoamide)
E2
+
SH SH
E3–FAD
E2
+
S
S
E3–FADH2
Mechanism of
Pyruvate Dehydrogenase
(Oxidation of E3–FADH2)
E3–FADH2 + NAD+ ——> E3–FAD + NADH + H+
Mechanism of Reoxidation of
Dihydrolipoamide
Page 574
Mechanism of Oxidation of E3–FADH2
Short Lived
Page 574
A Swinging Arm Transfers
Intermediates
E2
Page 575
Organization of E. coli
Pyruvate Dehydrogenase Complex
Pyruvate Dehydrogenase
(Formation of Acetyl-SCoA)
NAD+
NADH + H+
O
CH3
C
O
COOH
Pyruvate
+ CoenzymeA
SH
CH3
C
S
CoA + CO2
Acetyl–SCoA
Oxidative Decarboxylation
Regulation of
Pyruvate Dehydrogenase
• Product Inhibition (competitive)
– NADH
– Acetyl-SCoA
• Phosphorylation/Dephosphorylation
– PDH Kinase: inactivation
– PDH Phosphatase: activation
Regulation of PDH Kinase
(Inactivates PDH by phosphorylation)
• Activators of PDH Kinase
– NADH
– Acetyl-SCoA
• Inhibitors of PDH Kinase
–
–
–
–
Pyruvate
ADP
Ca2+ (high Mg2+)
K+
Regulation of PDH Phosphatase
(Activates PDH by Dephosphorylation)
• Activators of PDH Pase
– Insulin
– Mg2+
– Ca2+