CHAPTER 3 TCA CYCLE

Question 1

What are the 3 enzymes that make up the pyruvate dehydrogenase PDH complex?

Answer 1

1. Dihydrolipoyl transacetylase: 24 E2 prots
2. Pyruvate dehydrogenase: 24 E1 prots
3. Dihydrolipoyl dehydrogenase: 12 E3 prots

TOTAL 60 SUBUNITS

Question 2

Pyruvate dehydrogenase E1 function?

Answer 2

catalyze redox-decarboxyation reaction

Question 3

Dihydrolipoyl transacetylase E2

Answer 3

catalyze transfer of acetyl group

Question 4

Dihydrolipoyl dehydrogenase E3

Answer 4

reform oxidized version of lipoamide

Question 5

5 coenzymes that assist PDH complex reactions

Answer 5

1. thiamine pyrophosphate (TPP) bound to E1
2. Lipolic acid bound to E2
3. FAD bound to E3
4. CoA
5. NAD+

Question 6

4 steps of Pyruvate decarboxylase reaction

Answer 6

1. Decarboxylation
2. Oxidation-reduction
3. Acetyl-CoA formation
4. Regeneration of Lipoamide

Question 7

Multienzyme complex advantages

Answer 7

1. Enhances freq of interaction btw substrate & enz
2. Product of 1 rxn can be easily channeled to next enz (reduces side rxns)
3. All rxns can be coordinately controlled

Question 8

How are rxn intermediates channelled btw E2 (core of PyrDH complex) and E1 & E3 ptns on outside?

Answer 8

Lipoamide grp of E2
Lipolic grp attached to Lys residue of E2 has a long length (14Angstroms)
arm is connected to rest of E2 by residues that provide FLEXIBILITY
long arm picks intermediate from E1, brings to active site of E2 and swings pdt to E3
LIPOLIC ACID rxns can be inhibited by ARSENIC