PDH (pyruvate dehydrogenase) complex

a large enzyme complex that connects glycolysis to the TCA cycle. It converts pyruvate into acetyl-CoA which can enter the TCA cycle to produce energy

enzyme 1→ pyruvate dehydrogenase (PDH)

cofactor→ TPP (thiamine pyrophosphate)→ allows the enzyme to break the carbon bond safely and hold the remaining fragment

• removes CO2 from pyruvate (decarboxylation)

• stabilizes the 2-carbon fragment that remains after decarboxylation

• forms a hydroxyethyl intermediate

• pyruvate (3 carbon molecule) → 2 carbon fragment + CO2

enzyme 2→ dihydrolipoyl transacetylase (DLAT)

cofactors→ lipoic acid (lipoamide) and coenzyme A

lipoamide→ accepts the 2-carbon fragment from TPP and oxidizes it to an acetyl group which moves the reaction intermediate between enzymes inside the complex

coenzyme A→ accepts the acetyl group from lipoamide and forms acetyl-CoA which is the fuel that enters the TCA cycle

1) accepts the 2-carbon fragment from E1

2) oxidizes it to an acetyl group

3) transfers the acetyl group to CoA

• acetyl group + CoA → acetyl-CoA

enzyme 3→ dihydrolipoyl dehydrogenase (DLD)

cofactors→ FAD and NAD+

FAD→ accepts electrons from reduced lipoamide, resets the enzyme system so that the reaction can continue

NAD+→ accepts electrons from FADH2 and produces NADH which carries electrons to the electron transport chain where ATP is produced

1) reoxidizes the lipoamide cofactor

2) transfers electrons to FAD

3) transfers electrons to NAD+

• FADH2 +NAD+ → NADH

• produces NADH which later generates ATP in oxidative phosphorylation

products

acetyl CoA→ enters the TCA cycle

NADH→ goes to the electron transport chain

CO2→ released as waste