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

Glucose + 6 O2 ——> 6 CO2 + 6 H2O

∆Go’ = -200 kJ/mol

∆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

Figure 17-1

Oxidative Fuel Metabolism

Oxidation-Reduction Reactions:

Electron Transfer

Substrate —> NAD+ or FAD —> Electron Carriers —> O2

Electron Transport

Oxidative Phosphorylation

Figure 17-2

Citric Acid Cycle

Electron TransportOxidative Phosphorylation

ATP

H2O

ADP + Pi

Electron Transport[Proton Pumping]

Oxidative Phosphorylation

2 H+ + 1/ 2 O2Acceptor·H2

(NADH or FADH2)

Acceptor(NAD+ or FAD)

Substrate(oxidized)

Substrate·H2

(reduced)

Oxidized e– carrier

Reduced e– carrier

Etc.2 e–

Electron TransportOxidative 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

Acetyl-CoA

Thioester

Sources of Acetyl-CoA

• Carbohydrates (sugars via glycolysis)

• Fats (fatty acids)

• Proteins (amino acids)

Pyruvate Dehydrogenase(Formation of Acetyl-SCoA)

CH3 C COOH

O

CH3 C S

O

CoACoenzymeA SH

Acetyl–SCoAPyruvate

+ CO2

NADH + H+

+

NAD+

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

Figure 17-3a

Electron Micrograph of E. coli Pyruvate Dehydrogenase

Organization of E. coli Pyruvate Dehydrogenase Complex

Pyruvate Dehydrogenase(Mammalian Enzyme)

• E1, E2, and E3

• E3 binding protein

• Kinase (regulation)

• Phosphatase (regulation)

Table 17-1

Coenzymes and Prosthetic Groups of Pyruvate

Dehydrogenase

Thiamin Pyrophosphate

N

N

CH3

CH2 NS

CH3

CH2 CH2 O P O P O –

O O

O – O –NH2

Thiamin Pyrophosphate

N

N

CH3

CH2 NS

CH3

CH2 CH2 O P O P O –

O O

O – O –NH2

Lipoic Acid

HOOC (CH2)4

S S

Figure 17-7

Reduction of Lipoamide

E2

E2

Coenzyme A

HS CH2 CH2 NH C

O

CH2 CH2 NH C

O

CH

OH

C

CH3

CH3

CH2 OADP( 3'P)

Pantothenic Acid (vitamin B5)

NAD+

N

OCH2

OH OH

O

OCH2

OH OH

AOP

O

O–

P

O

O–

O

CNH2

O

Nucleotide

Nucleotide

Figure 14-12

Flavin Adenine Dinucleotide (FAD)

Reduction of FAD

N

N

N

NH

H3C

H3C O

O

CH2

CHOH

CHOH

CHOH

CH2OADP

N

N

N

NH

H3C

H3C O

O

CH2

CHOH

CHOH

CHOH

CH2OADP

H

H

2 H·

FADH2FAD

Pyruvate Dehydrogenase(Formation of Acetyl-SCoA)

CH3 C COOH

O

CH3 C S

O

CoACoenzymeA SH

Acetyl–SCoAPyruvate

+ CO2

NADH + H+

+

NAD+

Oxidative Decarboxylation

Overall Reaction ofPyruvate Dehydrogenase

Reaction order of Pyruvate Dehydrogenase

Mechanism of Pyruvate Dehydrogenase

(Decarboxylation of Pyruvate)

Same mechanism as Pyruvate Decarboxylase

CH3C OH

E1–TPP

+ E1–TPP

CH3C COOH

O

C

O O–

CO2

CH3C OH

E1–TPP

Pyruvate

Page 572

Mechanism of Decarboxylation of Pyruvate

Remainderof Reaction

Reaction order of Pyruvate Dehydrogenase

Mechanism of Pyruvate Dehydrogenase

(Hydroxyethyl Group Transfer)

CH3C OH

E1–TPPE2

S S

E2

S SH

C OH3C

+ E1–TPP+

H+

Forms of Lipoamide

Page 574

Mechanism of Hydroxyethyl Group Transfer

Reaction order of Pyruvate Dehydrogenase

Mechanism of Pyruvate Dehydrogenase

(Transesterification)

E2

SH SH

E2

S SHH3C C

O

SCoAC O

H3C

+CoA–SH+

Page 574

Mechanism of Transesterification

Reaction order of Pyruvate Dehydrogenase

Mechanism of Pyruvate Dehydrogenase

(Reoxidation of Dihydrolipoamide)

E2

SH SH

E2

S S

E3–FADH2+E3–FAD+

Mechanism of Pyruvate Dehydrogenase

(Oxidation of E3–FADH2)

E3–FADH2 + NAD+ ——> E3–FAD + NADH + H+

Page 574

Mechanism of Reoxidation of Dihydrolipoamide

Page 574

Mechanism of Oxidation of E3–FADH2

Short Lived

Page 575

A Swinging Arm Transfers Intermediates

E2

Organization of E. coli Pyruvate Dehydrogenase Complex

Pyruvate Dehydrogenase(Formation of Acetyl-SCoA)

CH3 C COOH

O

CH3 C S

O

CoACoenzymeA SH

Acetyl–SCoAPyruvate

+ CO2

NADH + H+

+

NAD+

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+