Inhibitors and Uncouplers

Table 1. Inhibitors of Respiration and Oxidative Phosphorylation

Site-Specific Target Complex

Carbon monoxide IVCyanide IVSodium Azide IVRotenone IAntimycin A IIIAmytal I

Phosphorylation

Oligomycin Fo

Uncouplers

2,4-Dinitrophenol (DNP) Proton gradientTrifluorocarbonylcyanide Phenylhydrazone (FCCP) Proton gradient

Any compound that stops electron

transport will stop respiration…this means you stop

breathing

Any compound that stops electron

transport will stop respiration…this means you stop

breathing

Electron transport can be stopped by

inhibiting ATP synthesis

Electron transport can be stopped by

inhibiting ATP synthesis

An uncoupler breaks the connection between

ATP synthesis and electron transport

An uncoupler breaks the connection between

ATP synthesis and electron transport

What is an Uncoupler?

Uncouplers break theconnection betweenelectron transport andphosphorylation

Electron transport is a motor

Phosphorylation is the transmission

Uncouplers let you put the car in NEUTRAL

Table 2. Action of Inhibitors on Respiration and Phosphorylation

Agent or Condition O2 uptake ATP synthesis

1. Inhibit electron transport……….

2. Inhibit phosphorylation………..

3. Increase proton gradient……….

4. Decrease proton gradient………

5. Add DNP………………………

6. Add Oligomycin……………….

7. Add Oligomycin + DNP………

O

NO2

NO2

2,4-dinitrophenol – a proton ionophore

H+

O

NO2

NO2

H O

NO2

NO2

H O

NO2

NO2

H+

Inner MembraneMatrix

Text p519Text p519

Brown Adipose Tissue

Uncouplinga proton gradientfrom FOF1 ATPaseProduces Heat! Thermogenin

Staying Alive Energy Wise

• We need 2000 Cal/day or 8,360 kJ of energy per day

• Each ATP gives 30.5 kJ/mole of energy on hydrolysis

• We need 246 moles of ATP

• Body has less than 0.1 moles of ATP at any one time

• We need to make 245.9 moles of ATP

• Each mole of glucose yields 38 ATPs or 1160 kJ

• We need 7.2 moles of glucose (1.3 kg or 2.86 pounds)

• Each mole of stearic acid yields 147 ATPs or 4,484 kJ

• We need 1.86 moles of stearic acid (0.48 kg or 1.0 pound of fat)

Controlof

Oxidative phosphorylation

What makes us breathe faster?

How does ATP synthesis in the mitochondria adjust to the needs of the cell?

[ATP][ADP][Pi] = ATP mass action ratio

Low: Energy debt, Signifies high ADP or low ATP

High: Energy sufficient, Signifies high ATP

HIGH Mass Action Ratio:

WHAT IS THE ATP MASS ACTION RATIO?

Oxidized cytochrome C [C3+] is favored

Cytochrome oxidase is low because of low C2+

O2 uptake lowLOW Mass Action Ratio:

Reduced cytochrome C [C2+] is favored

Cytochrome oxidase stimulated because of high C2+

Oxygen uptake high

ATP[ADP][Pi]

[NAD+][NADH]

½Keq =

[c2+][c3+]

½NADH + Cyt c (Fe3+) + ADP + Pi ½ NAD+ + Cyt c (Fe2+) + ATP Go’= 0

Control of Oxidative PhosphorylationControl of Oxidative Phosphorylation

EquilibriumEquilibrium

[ATP] can control its own production

Cytochrome c oxidase step is irreversible and is controlled byreduced cytochrome c (c2+)

Because of equilibrium, concentration of c2+ depends on [NADH]/[NAD+] and [ATP]/[ADP][Pi]

[c2+][c3+]

[NADH] [NAD+]

½ [ADP][Pi] [ATP]= Keq

NADH

ATP mass action ratioATP mass action ratio

Mass Action ration

NADH [c2+]/[c3+]

equilibrium

equilibrium

ADP [c2+]/[c3+]

ATP [c2+]/[c3+]

equilibrium

equilibrium

Cytochrome oxidase controls the rate of O2 uptake whichmeans this enzyme determines how rapidly we breathe.

Cytochrome oxidase controls the rate of O2 uptake whichmeans this enzyme determines how rapidly we breathe.

Control of Cytochrome Oxidase (Cox)

Stimulates Cox

Stimulates Cox

Stimulates Cox

Suppresses Cox

O2

O2 O :: O..

. ....

.Octet Rule

...

..O :: O. ..

Molecular Oxygen

= O2-

Unpaired electronUnpaired electron

Oxygen Radicals

Superoxide Anion

Partially reduced oxygen species

What is a Free Radical ?

Highly Reactive

Powerful Oxidant

Any chemical species with one of more unpairedelectrons…….

Short half life (nanoseconds)

Can exist freely in the environment

EXAMPLES OF FREE RADICALS

H. Hydrogen atom

O2 . Superoxide (oxygen centered)

.OH Hydroxyl radical (most reactive)

.NO Nitric Oxide

PRO-OXIDANTS (Generates Free Radicals)

Fe2+ + H2O2

Ascorbic acid + Fe2+

Paraquat

Agent Orange

Ozone

Generates hydroxyl radical

Generates hydroxyl radical

Generates hydroxyl radical

Generates superoxide radical

Generates superoxide radical

WHAT ARE ANTIOXIDANTS?WHAT ARE ANTIOXIDANTS?

ENZYMES

VITAMINS

Superoxide dismutase

Catalase

Peroxidases

O2-

H2O2

R-OOH

Vitamin E (tocopherols)

Beta Carotene (pro-vitamin A)

Vitamin C

Quiz 1

4 Questions

5 Points

1. Other than Fructose-6-PO4 and Fructose-1,6 bisPO4, name another phophate ester of fructose.

2. Other than glycerate-1,3 bisPO4, name another high energy intermediate derived from glucose in glycolysis.

3. Name a compound in the Krebs cycle, which when oxidized to CO2 and H2O gives rise to 30 ATPs

4. Name 2 pentoses that are found in the pentose phosphate pathway.

Fructose 1-PO4 or Fructose 2,6-bisPO4

PEP

Succinyl-CoA

Ribose-5-PO4 Ribulose-5-PO4 Xylulose-5-PO4