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Y Biochemistry 2 > Pyruvate Dehydrogenase Complex (Ben) > Flashcards

Pyruvate Dehydrogenase Complex (Ben) Flashcards

1
Q

What are the three metabolic enzymes involved in the PDH complex?

A

E1: Pyruvate Dehydrogenase

E2: Dihydrolipoyl Transacetylase

E3: Dihydrolipoyl Dehydrogenase

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2
Q

What is the first enzyme in the PDH complex and its prosthetic group?

A

Pyruvate Dehydrogenase

  • prosthetic group: Thiamine Pyrophosphate
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3
Q

What is the second enzyme in the PDH complex and its prosthetic group?

A

Dihydrolipoyl Transacetylase

  • prosthetic group: lipoic acid
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4
Q

Alone, PDH complex’s second enzyme’s prosthetic group has a different name than when it is bound to the enzyme.

What is it referred to as when bound and why?

A
  • PDH complex-bound lipoic acid is lipoamide

…because it binds to the amide group of a lysine side chain of the enzyme dihydrolipoyl transacetylase

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5
Q

What is the functional significance of how dihydrolipoyl transacetylase’s prosthetic group is bound?

A

the long lysine side chain to which lipoic acid is bound acts as a swinging arm…

it carries products and between the other two enzymes of the PDH complex

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6
Q

What is the 3rd enzyme of the PDH complex and what is its prosthetic group?

A

Dihydrolipoyl Dehydrogenase

  • prosthetic group: FAD
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7
Q

What is the first step of pyruvate’s oxidative decarboxylation via PDH complex?

Substrates?

Enzyme + prosthetic group?

Products?

A

Decarboxylation of…

Substrates: Pyruvate + H+

Enzyme/P Grp: Pyruvate Dehydrogenase + Thiamine Pyrophosphate (TPP)

Products: Hydroxyethyl-TPP + CO2

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8
Q

The 2nd step in the PDH complex contains two smaller steps.

What first happens to hydroxyethyl-TPP formed in step one?

Via what enzyme + P-group?

A

HETPP is oxidized via lipoamide (p-group)…

to acetyl-TPP…

leaving a reduced dihydrolipoamide

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9
Q

What is the second part of step 2 of the PDH complex reactions, acting on the dihydrolipamide + acetyl-TPP formed in part one?

What kind of special bond forms?

A

Acetyl group of acetyl-TPP transfers to…

…dihydrolipoamide, forming a high energy thio-ester bond and…

…creating acetyl dihydrolipoamide

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10
Q

What is the 2nd reaction which occurs associated with dihydrolipoyl transacetylase (E2 of PDH complex)?

Substrates?

Products?

A

An acetyl group transfer (hence transacetylase !!!)

Substrates: Acetyl-dihydrolipoamide + CoA-SH

Products: Acetyl-CoA + Dihydrolipoamide

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11
Q

What is the reaction associated with enzyme 3 of the PDH complex?

Substrates?

Enzyme + P Group?

Products?

A

Re-oxidation of lipoamide, reduction of FAD…

Substrate: Dihydrolipoamide

Enzyme/P-grp: Dihydrolipoyl Dehydrogenase + FAD

Products:

  • Lipoamide (oxidized)
  • FADH2 (not exactly a product, but rather the reduced version of the prosthetic group)
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12
Q

How is the prosthetic group of dihydrolipoyl dehydrogenase re-oxidized so that it can continue to function in the PDH complex cycle?

A

NAD+ accepts its electrons and is thus reduced to NADH

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13
Q

Where does the NADH formed by the PDH complex reactions go?

What pre-requirement does this place on PDH complex activity?

A

NADH fuels respiration

(no other reactions in the matrix significantly re-oxidize it)

  • this means PDH complex activtiy is coupled to respiration and is thus aerobic (even though it doesn’t use O2)
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14
Q

What happens to the acetyl-CoA formed by the PDH complex reactions?

(2 possible uses)

What is important about this acetylation step?

A
  1. further oxidation in the citric acid cycle
  2. lipid biosynthesis
  • this step can not be undone
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15
Q

How and to which enzymes of the PDH complex does allosteric regulation occur?

A
  1. Dihydrolipoyl acetyltransferase is inhibited by increased levels of acetyl-CoA
  2. Dihydroplipoyl dehydrogenase is inhibited by increased levels of NADH
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16
Q

How and to which enzyme(s) of the PDH complex does covalent modification regulation occur?

A

Pyruvate dehydrogenase (E1) is either phosphorylated (decreased activity) or dephosphorylated (increased activity) by…

PDH Kinase

PDH Phosphatase

17
Q

What activates PDH Kinase (and thus inhibits pyruvate dehydrogenase activity)?

A

increased levels of ATP, NADH, or Acetyl-CoA

18
Q

What inhibits PDH Kinase (and thus activates pyruvate dehydrogenase)?

A

increased levels of NAD+, Pyruvate, ADP, or AMP

19
Q

What activates PDH Phosphatase (and thus activates pyruvate dehydrogenase) ?

A

Insulin

or

Ca++ (as from working muscle)

Y Biochemistry 2 (24 decks)

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