Mammalian PDHC

Question 1

Where is PDHC occurring

Answer 1

• mitochondrial, so going to move pyruvate into the mitochondria, then feed the pyruvate through the PDH complex to form CO2 and water.
• complex has 3 enzymes present. (3 types, multiple copies)
• these enzymes are associated noncovalently

Question 2

What are the three enzymes in the complex?

Answer 2

1: Pyruvate DH (E1)
2: Dihydrolipoyl transacetylase (E2)
3: Dihydrolipoyl DH (E3)

Question 3

Complex structure

Answer 3

HUGE
Has core of 60 E2 monomers surrounded by 30-45 E1 heterotetramers and 12 E3 homodimers.

Size is the only way to take glycolytic pyruvate to convert to acetyl coA

• has additional subunits , E3BP which allows E3 and E2 to bind together. Also has 1-3 copies of PDH kinase and 1-3 copies of PDH phosphatase

Question 4

Thiamine Pyruvate (TPP)

Answer 4

Tightly bound to E1, decarboxylates pyruvate yielding hydroxyethyl-TPP.

Question 5

Lipoic acid (lipoamide)

Answer 5

covalently bound to E2 via lysine (swinging arm), accepts hydroxyethyl carbanion from TPP as acetyl group

Question 6

Coenzyme A (CoA)

Answer 6

dissociatable substrate for E2, accepts acetyl group from lipoamide

Question 7

FAD

Answer 7

tightly bound to E3, accepts pair of electrons from reduced lipoamide

Question 8

NAD

Answer 8

dissociable substrate for E3, accepts pair of electrons from reduced FADH2

Question 9

TPP thiazole ring

Answer 9

Thiazolium (TAZ) has positive charge N, loses a Hydrogen

Question 10

FAD structure

Answer 10

three fuzed heterocyclic system. FMN is not present in us, just FAD

Question 11

LIPOAMIDE

Answer 11

derived from lipoic acid, lysine attached to the R group which forms an amide…. when amine is added to carboxyl gets amide.
Given the appreviable L

Question 12

Dihydrolipoamide

Answer 12

LH2, disulfide broken

Question 13

acetyl-dihydrolipoamide

Answer 13

have one or both thiols forming a thioester… known as ACL