Pyruvate Oxidation to Acetyl CoA

Under anaerobic conditions, what can pyruvate be fermented into?

• In yeast: ethanol and CO2

• In muscle cells: Lactic acid

Pyruvate enters TCA cycle as… This only happens in what kind of conditions?

Acetyl-CoA. Aerobic!

Remember, fermentation occurs to…

Regenerate NAD+

Respiration produces ___ ATP than glycolysis alone. Evolutionarily, this gave organisms the chance to produce multicellular and more complex structures

More!

What is the final e- acceptor in cellular respiration?

O2

Respiration occurs in 3 major stages…

1. Acetyl CoA Production (Used pyruvate dehydrogenase complex)

2. Acetyl CoA Oxidation (TCA Cycle)

3. e- transfer and oxidative phosphorylation

Is anabolism or catabolism breaking things down?

Catabolism!

Respiration can also use __ and __ as a fuel to produce ATP. They all are converted into ___.

Fats and proteins. Acetyl-CoA

After glycolysis, the following steps of respiration occur in…

The mitochondria!

The oxidation of pyruvate to Acetyl-CoA is a __ carbon to __ carbon reaction.

3 carbon to 2 carbon.

Draw acetyl-CoA

Draw pyruvate

What are the 5 cofactors involved in pyruvate oxidation?

Lipoic acid, FAD, TPP (thiamine pyrophosphate), CoASH, NAD+

The PDC is very __. It is made of 3 kinds of peptides:

Complex. E1, E2 and E3

Pyruvate oxidation occurs in what partof the mitochondria?

Matrix!

PDC is inhibited by __ and __

NADH and GTP (can interconvert to ATP)

High energy states

PDC is stimulated by ___.

Insulin (high glucose state)

What cofactors does E1 use?

Thiamine pyrophosphate

What cofactors dos E2 use?

Lipoate, CoA

What cofactors does E3 use?

NAD+, FAD

E1:E2 ratio is…

1:1

E1/E2:E3 ratio is…

2:1

Describe the structure and relative positioning of the enzymes making up the PDC

Lipoyl domain connects E1 and E2 → needed for physical transfer of a substrate later in the rxn

Lipoyllysine has 3 forms….

Oxidized lipoyllysine, acetyl and reduced

E3’s primary function is to…

Regenerate oxidized lipoyllysine by reducing NAD+

E1is called __. E2 is called __. E3 is called __.

1. Pyruvate dehydrogenase

2. Dihydrolipoyl transacetylase

3. Dihydrolipoyl dehydrogenase

What is the functional part of TPP?

The thiazolium ring

What happens to the thiazolium ring so it can attack pyruvate?

It gets deprotonated and forms a carbanion

Which carbon does deprotonated TPP attack?

The carbonyl

After TPP attacks pyruvate, what happens?

A decarboxylation which releases CO2 and leaves a 2 carbon intermediate covalently attached to the thiazolium ring

After the decarboxylation step with TPP, what happens?

Resonance changes the structure from an enol to an alcohol. Then, a proton is added to neutralize the compound, which leaves us with hydroxyethyl-TPP, and it is ready to interact with E2

Draw hydroxyethyl-TPP

What does the oxidized lipoic acid cofactor do with hydroxyethyl-TPP?

It picks up the hydroxyethyl and frees the TPP, so E1 can act on the next incoming pyruvate

What is E2 called when it picks up the hydroxyethyl?

Acylated form

What happens after the lipoic acid grabs the hydroxyethyl group?

A free-floating CoA’s thiol group (-SH) attacks the carbonyl C of the 2 carbon intermediate, and releases Acetyl-CoA off of E2. This process reduces Lipoic acid.

What is the function of E3?

It regenerates oxidized lipoic acid by having FAD+ get reduced to FADH2.

How is FAD+ regenerated on E3?

FADH2 transfers a proton to NAD+, which also releases 1 proton into solution. NADH is formed.

CoA is __ __ in the mitochondtial matrix

Free floating

What is the important reactive group on CoA?

The thiol group

CoA and Lipoic acid have what are called…

Swinging thiol groups

Lipoic acid is conjugated to E2 via a __ residue

Lys

Draw the oxidized business end of Lipoic acid (poised to pick up 2 carbon compound)

Draw the acylated business end of Lipoic acid

Draw the reduced business end of lipoic acid