Lecture 7 BCH 3120 - ATP Synthesis + Oxidative Phosphorylation uncoupling

ATP synthase

Complex V, converts energy from proton gradient into ATP

ATP Synthase Structure

F0F1 complex

F0 unit of ATP synthase

portion of ATP synthase embedded in the membrane. Proton turbine

- 8-15 c subunits (c-ring)

- a subunit (channel)

- 2 b subunits

F1 unit of ATP synthase

Subunits not bound to the membrane. ATP synthase activity

- (𝛼β)3 (3 dimers)

- 𝛾

- 𝛿

- ε

Binding change model of ATP synthase

Since the 𝛾 subunit is asymmetric, when it turns it will make different contacts with 𝛼β subunits, causing the three dimers to be in different conformation depending on the rotation of 𝛾

Rotor - ATP synthase

moving units

- c-ring

- 𝛿

- ε

- 𝛾

Stator

Stationary units

- a

- b

- the 3 𝛼β dimers

Flow of protons through ATP synthase

- protons enter through the channel (subunit a)

- proton binds 1 c subunit

- this causes the c-ring to turn

- when the proton makes a full turn it exits the a channel into the matrix

Each c subunit can bind --- proton(s)?

one

αβ dimer conformations

Open → Loose → Tight

O conformation

open site, releases ATP

L conformation

loose binding to ADP

T conformation

tight binding to ATP

ATP is formed in which conformation?

T conformation

Proton to ATP ratio

4 protons are needed to generate 1 ATP

- (1 used to transport Pi into the matrix and 3 to drive the ATP synthase)

NADH ATP yield

2.5 ATP

FADH2 ATP yield

1.5 ATP

Why does NADH need a shuttle?

The inner mitochondrial membrane is not permeable to NADH

2 NADH shuttles

1. Glycerol 3-phosphate shuttle

2. Malate-Aspartate shuttle

Glycerol 3-phosphate shuttle is used where in the body?

muscles and brain

malate-aspartate shuttle is used where in the body?

liver, kidney, and heart

Malate-Aspartate shuttle - step 1

Reduction of OAA into malate by malate dehyrogenase using NADH

Malate-Aspartate shuttle - step 2

Transport of malate into mitochondrial matrix by the malate-𝛼-ketoglutarate transporter

Malate-Aspartate shuttle - step 3

oxidation of malate into OAA by malate dehydrogenase using NAD+

(NADH now in the mitochondria)

Malate-Aspartate shuttle - step 4

transamination of OAA into asp by the aspartate aminotransferase (transaminase)

Malate-Aspartate shuttle - step 5

transport of asp outside the mitochondria by the glutamate-aspartate transporter

Malate-Aspartate shuttle - step 6

transamination of asp into OAA into asp by transaminase

Glycerol 3-phosphate shuttle - step 1

DHAP is reduced to glycerol 3-phosphate by the cytosolic glycerol 3-phosphate dehydrogenase using electrons from NADH

Glycerol 3-phosphate shuttle - step 2

glycerol 3-phosphate enters the intermembrane space

Glycerol 3-phosphate shuttle - step 3

Glycerol 3-phosphate is re-oxidized into DHAP by the mitochondrial glycerol 3-phosphate dehydrogenase

Where are electrons from the Glycerol 3-phosphate shuttle stored?

On FAD to form FADH2

What complexes of the ETC does the Glycerol 3-phosphate shuttle bybass?

Complex I, and II

Oxidative phosphorylation uncoupling

when protons are returned to the matrix by other means then the ATP synthase

What are the 2 types of oxidative phosphorylation uncouplers?

Chemical uncouplers

Endogenous uncoupling proteins

Thermogenin (UCP1)

endogenous uncoupling protein

- found in inner mitochondrial membrane

Where is thermogenin expressed?

Brown adipose tissue

What does thermogenin allow?

Production of heat through proton dissipation

- non-shivering heat production

2,4-dinitrophenol (DNP)

chemical uncoupler

- transports protons across the membrane; able to cross it easily

DNP allows for?

heat production

DNP side effects

blindness, hyperthermia, death

Complex I inhibitor

Rotenone

Rotenone use

pesticide, insecticide, etc.

Complex III inhibitor

Antimycin A

Complex IV inhibitor

cyanide and carbon monoxide