Citric acid cycle

Production of acetyl-CoAReactions of citric acid cycle

Regulation of the citric acid cycle

Oxidative decarboxylation

P. 602

Production of acetyl-CoA is catalyzed by a large enzyme complex

NAD+ O IICH3-C-S-CoA

CoA-SH

TPP-CHOH-CH3

CO2

pyruvate

Reactions catalyze by PDH (pyruvate dehydrogenase

complex)

Pyruvate dehydro-genase

(E1)

TPP

LysDihydrolipoyl

transacetylase(E2)

(o)lipoate O

II

CH

3 -C-lipoate (r)lipoate

Acetyl-CoA

E3

FADH2FAD

NADH

TPP lipoate CoA FAD NAD+

P. 570

Pyruvate dehydrogenase complex

• Pyruvate dehydrogenase complex includes three enzymes: pyruvate dehydrogenase (E1), dihydrolipoyl transacetylase (E2), and dihydrolipoyl dehydrogenase (E3) and also five coenzymes.

P. 513NAD+

CAC

TPP

p.541

PDH

P. 516FAD and FMN

PDH

P. 603

Coenzyme A (CoA)

PDH

P. 603

Lipoic acid (lipoate)

• Together with lysine of E2, the lipoyllysyl arm has enable the E2 becoming more flexible in terms of catalyzing reactions.

PDH

The citric acid cycle

oxaloacetate

Acetyl-CoA

H2O

CoA-SHCitrate

isocitrate

H2OH2O

cis-aconitate

citrate

cis-aconitate

isocitrate NAD+

NADHCO2-ketoglutarate

-ketoglutarate

NAD+

CoA-SH

CO2NADHSuccinyl-CoASuccinyl-CoA

GDP(ADP)

GTP(ATP)

Pi

CoA-SHSuccinate

SuccinateFAD

FADH2Fumarate

Fumarate

malateH2O

malate

NAD+NADHoxaloacetate

Citrate synthase

aconitase

aconitase

Isocitrate dehydrogenase

a-ketoglutarate dehydrogenase

complex

Succinyl-CoA synthetase

Succinate dehydrogenase

Fumarase

Malate dehydrogenase

p617Citric acid cycle components are important biosynthetic intermediates

Anaplerotic reactions of citric acid cycle

Regulation of citric acid cycle