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Biochemistry I > Chapter 12: The Pyruvate Dehydrogenase (PDH) Complex > Flashcards

Chapter 12: The Pyruvate Dehydrogenase (PDH) Complex Flashcards

1
Q

Cytoplasmic pyruvate

A
  • Must enter the mitochondria
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2
Q

Metabolism converges on

A
  • The pyruvate dehydrogenate complex
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3
Q

Control of pyruvate dehydrogenase activity

A
  • Inactivation by phosphorylation (eukaryotes only)
  • Activation by dephosphorylation
  • Allosteric control
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4
Q

PDH multienzyme complex

A
  • Three non-covalently linked enzymes
  • Two regulatory enzymes (kinase and phosphatase)
  • Five cofactors
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5
Q

Three non-covalently linked enzymes of PDH complex

A
  • Pyruvate dehydrogenase (E1)
  • Lipoate acetyltransacetylase (E2)
  • Lipoamide dehydrogenade (E3)
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6
Q

Five cofactors of PDH complex

A
  • Thiamine pyrophosphate (thiamine = Vitamin B1)
  • Lipoic acid
  • Flavin adenine dinucleotide
  • Coenzyme-A (CoA-SH)
  • NAD+
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7
Q

Thiamine pyrophosphate (TPP)

A
  • Decarboxylates pyruvate

- Yields a hydroxyethyl-TPP carbanion

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8
Q

Lipoic acid

A
  • Accepts the hydroxoethyl carbanion from TPP as an acetyl group
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9
Q

Coenzyme-A (CoA)

A
  • Accepts the acetyl group from lipoamide
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10
Q

Flavin adenine dinucleotide (FAD)

A
  • Reduced by lipoamide
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11
Q

Nicotinamide adenine dinuleotide (NAD+)

A
  • Reduced by FADH2
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12
Q

Oxidative decarboxylation of pyruvate catalyzed by

A
  • Pyruvate dehydrogenase
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13
Q

Pyruvate translocase

A
  • Helps pyruvate across the inner mitochondrial membrane
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14
Q

Pyruvate that is not phosphorylated can pass through membrane

A
  • By diffusion

- Using a specific translocase

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15
Q

Overall PDH Reaction

A
  1. Oxidative decarboxylation
  2. Pyruvate is oxidized > forms Acetyl-SCoA and O2
  3. NAD+ is reduced to form NADH and H+
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16
Q

Reaction mechanism of PDH complex

A
  1. Decarboxylation of pyruvate
  2. Oxidation of hydroxyethyl TPP
  3. Acetyl-SCoA formation
  4. Oxidation of lipoamide
17
Q

2 different fates of pyruvate in metabolism

A
  • Converted to Acetyl-CoA

- Used as a substrate for gluconeogenesis

18
Q

Options when pyruvate’s fate is conversion to Acetyl-CoA

A
  • Enter CAC > degraded and production of energy

- Used in fatty acid biosynthesis

19
Q

Purpose of pyruvate when it becomes a substrate for gluconeogenesis

A
  • Used for the synthesis and storage of glycogen
20
Q

PDH step is irreversible

A
  • Commits carbon atoms of glucose to CAC or FA synthesis
21
Q

Acetyl-SCoA (breakdown product of fatty acids)

A
  • Cannot be used in gluconeogenesis because pyruvate is irreversible
22
Q

Oxaloacetate can be used to

A
  • Make glucose during starvation
23
Q

Turns on the PDH complex

A
  • Dephosphorylation
24
Q

Covalent phosphorylation at 3 serine residues inhibits

A
  • The PDH complex
25
Q

Mg++ dependent kinase

A
  • In mammals not prokaryotes
  • Stimulated by ATP, acetyl-SCoA, and NADH
  • Inhibited by pyruvate and ADP
26
Q

Activation by dephosphorylation

A
  • Ca++ dependent phosphatase

- Favored by insulin in fed state

27
Q

Allosteric inhibition of PDH complex by

A
  • ATP
  • NADH (product)
  • Acetyl-SCoA (product)
28
Q

High levels of product

A
  • Inhibit PDH

- Promote phosphorylation

29
Q

High levels of substrate

A
  • Stimulate PDH

- Inhibit phosphorylation

30
Q

When insulin activates a PDH phosphatase

A
  • Increases PDH activity
31
Q

Covalent modification of eukaryotic pyruvate dehydrogenase

A
  • Specific phosphorylation of serine residues on E1
32
Q

Thiamine deficiency/Beriberi (pyruvate oxidation disorder)

A
  • Cofactors not available
  • Involves vitamin B1
  • Neurological symptoms: limb paralysis, cardiac insufficiency, and enlarged heart
33
Q

Arsenic or mercuric poisoning (pyruvate oxidation disorder)

A
  • Cofactors are disabled

- Prokaryotic enzyme more sensitive

34
Q

Genetic diseases

A
  • May cause PDH to be absent or defective
  • Lactate acidosis
  • Ataxia, lethargy, poor visual tracking, and tachycardia
35
Q

Arsenic poisoning

A
  • Arsenite and organic arsenical bind to sulfhydryl compounds
  • Lipoamide containing enzymes include PDH and alpha-ketoglutarate dehydrogenase & glyceraldehyde-3-P dehydrogenase
  • Uncouples oxidative phosphorylation
  • More toxic to microbes
36
Q

Allosteric activation of PDH complex by

A
  • AMP
  • CoA
  • NAD+
37
Q

Oxidative decarboxylation of pyruvate occurs in

A
  • The mitochondrial matrix
38
Q

Major, but not only source of Acetyl-SCoA

A
  • Oxidative decarboxylation of pyruvate

Biochemistry I (34 decks)

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