pyruvate dehydrogenase complex

Question 1

what is pyruvate dehydrogenase complex (PDC)?

Answer 1

it is one of the largest multi-enzyme, supramolecular machines.
its found in prokaryotes and eukaryotes
it serves a strategic role in metabolism

Question 2

what is in the matrix of mitochondria?

Answer 2

its an internal space containing enzymes of the TCA cycle and oxidative decarbonisation of pyruvate

Question 3

what is in the inner membrane of the mitochondria?

Answer 3

it’s a large surface of cristae with proteins of the electron transport chain, ATP synthase, transport proteins, and electrochemical gradient of H+ ( which drives pyruvate and phosphate uptake)

Question 4

what is at the outer membrane of the mitochondria?

Answer 4

channel proteins (porin), molecules up to 5kDa can enter the intermembrane space

Question 5

what is the name of the irreversible like from glycolysis to the TCA cycle?

Answer 5

pyruvate dehydrogenase, it is oxidative decarbonisation and is a type of REDOX reaction.

Question 6

when and where does mitochondrian oxidative decarbonisation of pyruvate occur?

Answer 6

it occurs in the mitrochondria, where carbon atoms of the carbohydrates and amino acids are oxidised via the TCA cycle or to the synthesis of fatty acids
it only occurs if ATP is needed or if two carbon fragments are needed for fatty acid biosynthesis
controlled both allosterically and by phosphorylation

Question 7

what are the stages of mitochondrial oxidative decarbonisation of pyruvate?

Answer 7

1. decarbonisation of pyruvate (3C) to a 2-carbon alcohol
2. oxidation of the alcohol to an acid (with reduction of NAD+ to NADH)
3. esterification to coenzyme A

Question 8

what are the three subunits and 5 cofactors in pyruvate dehydrogenase?

Answer 8

the 3 subunits

• pyruvate dehydrogenase (E1)
• dihydrolipoamide acetyltransferase (E2)
• dihydrolipoamide dehydrogenase (E3)

the 5 cofactors
-thiamine pyrophosphate TPP
-lipoamide
-coenzyme A
-FAD
-NAD+
Mg2+

Question 9

what are the prosthetic groups of pyruvate dehydrogenase?

Answer 9

• thiamine pyrophosphate (TPP)
• lipoic acid
• flavin adenine dinucleotide (FAD)

Question 10

what allows the coordinated catalysis of the reaction?

Answer 10

the structural integration of three enzymes and the long, flexible lipoamide carrying arm allows the coordinated catalysis

Question 11

why cant animals convert acetyl CoA into glucose?

Answer 11

as a carbon of glucose is either committed to- oxidation of CO2
- incorperated into lipid

Question 11

why cant animals convert acetyl CoA into glucose?

Answer 11

as a carbon of glucose is either committed to- oxidation of CO2

Question 11

why cant animals convert acetyl CoA into glucose?

Answer 11

as a carbon of glucose is either committed to- oxidation of CO2

Question 12

what is pyruvate dehydrogenase regulated and inhibited by?

Answer 12

regulated allosterically

• inhibited by NADH and acetyl CoA
• activated by NAD+ and CoA-SH

inhibited by phosphorylation on E1

• PDH kinase activated by ATP, NADH and acetyl CoA
• ” “ inhibited by ADP and pyruvate
• PDH phosphatase activated by an increase in [Ca2+]

Question 13

what is the advantage of a multienzyme complex?

Answer 13

• its a group of non-covalently associated enzymes that catalyse two or more sequential steps in a metabolic pathway
• used for metabolic channeling
• direct transfer of a metabolite from one enzyme to another avoids dilution of metabolite in the aqueous enviroment and increases the rate of reaction so the diffusion of the substrate is not rate-limiting

Question 14

what are the 6 major components of human PCD?

Answer 14

pyruvate dehydrogenase (E1) 
dihydrolipoyl acetyltransferase (E2)
dihydrolipoyl dehydrogenase (E3)
E3-binding protein (E3BP)

pyruvate dehydrogenase kinase (PDK)
pyruvate dehydrogenase phosphatase (PDP)

Question 15

how does E2 work as a scaffold to organise and connect the different components?

Answer 15

L1 and L2 are connected by alanine-proline linkers , the outer linker region allows a “swinging arm” active site coupling mechanism between the E1, E2 and E3 components
the lipoic acid prosthetic group can extend into the active-site channels and perform the substrate channeling C-terminal part of the inner catalytic domain

Question 16

what are the variations in E2 that are species depandant?

Answer 16

the no. of lipoyl domains per E2 subunit can be 1 ( yeast, chloroplast, Bacillus stearothermophilus),
two (mammalian, plant mitochondria, and Streptococcus faecalis), or
three (Escherichia coli or Azotobacter vinelandii)

the ability to bind to E1 and/or E3
in eukaryotes it only binds to E1
in bacteria it can bind to E1 or E3