BIOENERGETICS:OXIDATIVE

PHOSPORYLATIONStudent Edition 10/23/14 Version

Pharm. 304 Biochemistry

Fall 2014

Dr. Brad Chazotte 213 Maddox Hall

chazotte@campbell.eduWeb Site:

http://www.campbell.edu/faculty/chazotte

Original material only ©2000-14 B. Chazotte

Goals• Learn the basic tenets of the chemiosmotic hypothesis and how mitochondrial

structure is consistent with the hypothesis.

• Consider how thermodynamics describes electrochemical gradient & oxidative phosphorylation.

• Learn the quantitative description of the proton electrochemical gradient and its components. Be able to calculate the phosphorylation potential.

• Be able to calculate the free energy of hydrolysis.

• Learn the basic components involved in pumping proton across the mitochondrial inner membrane. Understand the concept and meaning of the P:O ratio.

• Learn the structure of the F1Fo-ATPase and how Boyer’s binding exchange involves this structure in the synthesis of ATP.

• Understand how fluorescent dyes can report on the (mitochondrial) membrane potential in living cells and how changes in the potential due to substrates and inhibitors can be monitored.

• Understand how gradients involve the use or storage of energy.

CHEMIOSMOTIC HYPOTHESISTenets

1. Energy transducing membranes are vesicular, sealed, and impermeable to protons except for the pathways involved in redox mediated or protein-catalyzed H+ translocation.

2. Energy is stored in a pH gradient or membrane potential which are energetically equivalent, with the electrochemical potential.

3. The Dm +H is formed by vectorially alternating H+ and e- carriers in the electron transport chain.

4. An H+ flux is coupled to the ATP synthase/ATPase catalyzed by the large multisubunit F0F1 ATPase. Each reaction is anisotropic with respect to this flux. The synthesis reaction is coupled to an H+ flux driven by the DmH+ from the DmH+–positive side of the membrane.

5. Uncouplers of energy transduction were predicted to be lipid-soluble weak acids or bases that can catalyze the equilibration of H+ of OH- across the membrane.

Cramer & Knaff 1990

THERMODYNAMICSBrief Description

Chemical Work and Chemical Potential

The chemical potential mi, of compound I, is the free energy per mole

G

ni T, ,p, ,nj ni mi

is the partial derivative with respect to ni when temperature, pressure, and other n are held constant.

m is important for transport problems because it is the change in free energy of a system per mole of component moved in or out of the system.

Cramer & Knaff 1990

Proton Electrochemical Gradient (H+) #1

The electrochemical difference of protons across the mitochondrial inner membrane provides the high energy state to drive ATP synthesis, ion and substrate transport, transhydrogenation, and other energy requiring reactions.

One can write for hydrogen transport across, e.g., the mitochondrial inner membrane, where F= Faraday constant and = DY membrane potential in mV

DmH+= F DY – 2.303 RT log (Hi+/Ho

+)

DmH+= F DY – 2.303 RT DpH

H+ is composed of two components:

a membrane potential (charge difference; electrical potential):

a pH gradient (concentration difference; chemical potential): pHIn mitochondria is the bulk of the contribution to H+

Components of Mitochondrial Proton Gradient

Topic:OxPhos Alberts et al Fig 14-19

Proton Electrochemical Gradient (H+) #2

H+ = F - 2.303 RT pHF =Faraday constant = 96,487 coulombs/mole = 96.5 kJ mol-1 V-1 = 23.06 kcal mol-1 V-1

R = gas constant = 8.3143 J deg-1 mol-1 = 1.9872 cal deg-1 mol-1 = 0.082056 liter atm

deg-1 mol-1 T = absolute temperature

Represents the free energy change in kJ/mole when 1 mole of H+ moves into the mitochondrion.

Expressing the proton electrochemical gradient in millivolts is called the phosphorylation potential ( p).

p= H+ / F = - 2.303 (RT/F) pH

is the bulk of the contribution to H+

Determination of pH

• Calculate from equilibrium distribution of weak bases.

• Use Henderson-Hasselbalch equation

[HA]in = [HA]out @ equilibrium

K a = ([H+]in [A-]in)/[HA]in = ([H+]out [A-]out)/[HA]out

pH = log([A-]in / [A-]out)

Note: mitochondrial pH is typically less than 1 pH unit

Calculation using Phosphorylation Potential pProblem: Calculate the pH gradient at 37 ºC required across the mitochondrial

inner membrane to equal a membrane potential of -150 mV. The relevant equation for the phosphorylation potential in mitochondria, which

is in mV units already, is:

p = H+ / F = - 2.303 (RT/F) pH  0 = -150 mV - 2.303 (8. 3143 J deg-1 mol-1*310.15 ºK/96.5 kJ mol-1 V-1) pH

  0 = -150 mV - 2.303 (8. 3143 J deg-1 mol-1*310.15 ºK/96,500 J mol-1 V-1) pH

0.150 V = - 2.303 (2.672*10-2 V-1) pH0.150 V = - 0.0616 V-1 pH

  pH = -2.44

Proton Motive Force in Oxidative Phosphorylation

Horton et al 2012 Figure 14.9

Uses of the Proton Gradient

Berg, Tymoczko, & Stryer 2012 Fig 18.44

PROTON PUMPING & OXIDATIVE PHOSPHORYLAYION

Schematic of Electron Transport Enzyme Complexes

H+ ions transported across a membrane per unit area to generate = 100 mV

= Q/C where C is the specific membrane capacitance. Q is the charge per unit area.

For biological membranes C ~ 1 farad/cm2.

Thus, if = 0.1V and C= 10-6 coulombs/cm2, Q = 1.0 10-7 coulombs/cm2.

Charge on one proton = 1.6 10-19 coulombs

# protons translocated per unit area = 6 x 1011/cm2.

# protons translocated per sq micron = 6 x103

For a 300 Å diameter vesicle the translocation of 20 protons would generate a 100 mV potential.

For a typical rat liver mitochondrion estimate:

6 x 1011 protons /cm2 520.6 cm2/mg protein 8.7 x 109 mitochondria/mg protein = 35,903 protons/mitochondrion

Cramer and Knaff 1990

“THE” CHEMIOSMOTIC EXPERIMENT

Berg, Tymoczko, & Stryer 2012 Fig 18.23

Factors Controlling the Partition of p Components and pH

Nicholls & Ferguson Bioenergetics 2 1992

Proton Pumping in Electron Transport

Lehninger 2000 Fig 19-15

Lehninger 2000 Fig 19-16

Topic:Electron Transport

OXPHOS OVERVIEW

Lehninger 2000 Fig 19-11

Q Cycle Schematic

Voet, Voet, & Pratt 2013 Fig 18.15

Control of Oxidative Phosphorylation

P: O Ratios Revisited in the Chemiosmotic World

P:O, ATP:O, ATP/2e-, 2H+/e- !

The ratio of electrons transported to hydrogen ions pumped is an important number in oxidative phosphorylation.

It is generally agreed now that FOUR protons are consumed to produced 1 ATP. One of those protons is used in transporting ATP, ADP and Pi.

P:O Ratios in Electron Transport

Voet, Voet & Pratt 2006 pp577-578

ATP synthesis is tightly coupled to the proton gradient.

Possible to express the amount of ATP synthesized in terms of the substrate molecules oxidized.

Experiments had shown approximately 2.5, 1.5 , and 0.5 ATP synthesized with oxidations of NADH (via complex I), FADH2 (via complex II) and TMPD (via Complex IV, artificial 2e- donor).

P:O ratio relates amount of ATP synthesized to amount oxygen reduced.

Years of controversy over ratios. Integer or non-integer. Likely non-integer. Chemiosmotic hypothesis unlike other theories does not need whole numbers.

Mitochondria Redox States

(according to Chance and Williams [Adv. Enz. 17 1956]) [O2] ADP Substrate Respiration

Limiting

State 1 >0 low low slow ADP

State 2 >0 high ~low slowsubstrate

State 3 >0 high high fast e-trans

State 4 >0 low high slow ADP

State 5 0 high high 0 oxygen

Oxidative phosphorylation is occurring during state 3 respiration

Polarographic Determination of P/O Ratio

State 1

State 4

State 3

State 5

COMPONENTS INVOLVED IN OXIDATIVE

PHOSPHORYLATION

[DIRECTLY & INDIRECTLY]

F1F0 ATP Synthase Polypeptide Structure

Ref:Sarasate Fig 5 Science 283 1999Voet, Voet, & Pratt 2013 Fig 18.22 (inverted)

OXIDATIVE PHOSPHORYLATION:

ATP Synthase Binding Model

Topic: OxPos

Lehninger 2000 Fig 19-23 Topic:Ox Phos

ATP Synthase Binding Site Model

3

1

2

1

Voet, Voet & Pratt 2008 Figure 18.24

O - catalytically inactive & very low ligand affinity

L – catalytically inactive & loose ligand binding

T – catalytically active & tight ligand binding

1) ADP & Pi bind to site “L”

2) “L” converted to “T” site by energy driven conformational change

3) ATP is synthesized at site “T” and release as “T” becomes “O” site during energy driven conformational change

3-αβ “subunit pairs” in F1. β binds nucleotide

ATP Synthase (F1F0) Structure

Voet, Voet & Pratt 2002 Figure 18.26

Negative Stain EM

Cryo EM (F1F0 E. Coli)

Artist Illustration

Voet, Voet & Pratt 2013 Fig 18-28

Topic:Ox Phos

Proof of ATP

Binding Model

Fo

F1

OXIDATIVE PHOSPHORYLATIONADP/ATP Translocator 1

Horton et al 2012 Fig 14.20 Topic: OxPhos

ADP-ATP Translocator: Conformational Mechanism

Voet, Voet & Pratt 2008 Figure 18.6

Lehninger 2000 Fig 19-25

Topic:Electron Transport

OXPHOS TRANSPORTER RELATIONSHIPS

e- Transport & Oxidative Phosphorylation

Lehninger 2000 Understand Biochemistry CD

MITOCHONDRIAL OxPhos Free Energy of Hydrolysis in a Cell

Lehninger 2000 Table 14-5 Topic:OxPhos

G°´= –30.5 kJ/mol for ATP. However, that is based on standard conditions, i.e. 1 molar. pH 7.0, which may not be the conditions in a living cell. Consider a human erythrocyte

Free Energy of Hydrolysis in a Cell. II

Lehninger 2000 Box 14-2 Topic:OxPhos

[ADP]1 [Pi]1

DGp = DG ´ + 2.303RT log K´eq = DG ´ + 2.303RT log [ATP]1

[2.50 x 10-4]1 [1.65 x 10-3]1

= -30,500 J mol –1 + 2.303 x 8.315 J mol –1 K -1 x 298 K * log [2.25 x 10-3]1

= - 30,500 J mol –1 + (5,707 J mol –1 x -3.737)

= - 30,500 J mol –1 – 21,327 J mol –1

= - 51,827 J mol –1 for hydrolysis

and 51,827 J mol –1 for ATP synthesis

Nernst Equation

= -(RT/F) ln(Ain / Aout)

Which at room temperature simplifies to

= -59 ln(Cin / Cout)

= the membrane potential

Ax = probe chemical activity inside or outside

R = gas constant T = absolute temperature

F = Faraday constant

Cx = the probe concentration inside or outside

Calculation using the Nernst EquationGiven: TMRM concentration = 50 mM inside and 5 nM outside the

mitochondrion at 37 C

= - (RT/F) ln(Cin / Cout)

= - (8.315 J mol –1 K -1 x 310 K / 96,500 J mol-1 V-1 ) ln(50 µMin / 5nMout)

= - (8.315 J mol –1 K -1 x 310 K / 96,500 J mol-1 V-1 ) ln(50 µMin / 5nMout)

= - (8.315 J mol –1 K -1 x 310 K / 96,500 J mol-1 V-1 ) ln(10,000)

= - (2,477.87 J mol –1 / 96,500 J mol-1 V-1 ) 9.210

= - (0.0267 V ) 9.210 = -0.246 V = - 246 mV

6AP16076

Nucleus

Graylevel Image

Confocal Image of Human Fibroblast Labeled with TMRM

Cytoplasm

Mitochondrion

Pseudocolored Image

6AP02123

ROI

Platelet Mitochondria

Mononuclear Leukocyte

based Pseudocolored ImageGraylevel Image

Selecting a Region of Interest to HistogramHuman Mononuclear Leukocyte

Selected Inhibitors of Mitochondrial Bioenergetics

• CCCP collapses pH and • Valinomycin collapses • Rotenone inhibits Complex I electron transport.• Antimycin a inhibits electron transport at Complex III• TTFA inhibits Complex II electron transport.• KCN inhibits electron transport at Complex IV• Oligomycin prevents ATP synthesis, increases • 2-Deoxyglucose causes mitochondrial respiratory jump

6MA13087

6MA13088 CCCP

CCCP Effects

HMINH1

Effects of Mitochondrial Inhibitors on IPDs of Human Mononuclear Leukocytes

2.8 M, 29 g/ml, 0.87 M

BIOENERGETICS OF CELLULAR TRANSPORT

Topic: Bioeneregtics Transport

Thermodynamics of Ion Gradient

For protons we have written:

H+ = o +zF + 2.303 RT log (H+)

Likewise for a electrochemical sodium gradient we can write

Na+ = zF + 2.303 RT log (Na+final)

(Na+initial)

= the membrane potential, R = gas constant, T = absolute temperature, F = Faraday constant, z = charge (for proton: z = +1)

Cramer & Knaff 1990 pp18-19

Lehninger 2000 Fig 12-29

Active Transport Processes Driven via the Mitochondrial Gradient

Topic:OxPhos Alberts et al Fig 7-21

Thermodynamics of H+–Linked Active TransportSymport

If all of the free energy available in the H+ is stored in the electrochemical potential, then we can write for Dms of substrate accumulation in a symport mechanism. Where S refers to a solute molecule and n protons to transport one solute molecule

Gtotal = n* H+ s = 0 eq 1

DmH+= F DY + 2.303 RT log (Hi+/Ho

+) eq 2

Dms= zF + DY 2.303 RT log (Si+z/So

+z) eq 3

Where “i” is inside and “o” outside & for solute the initial state is outside and the final state is

inside = DY Yi -Yo; then Substituting eqs 2 & 3 into eq 1

0= zF + DY 2.303 RT log (Si+z/So

+z) + F DY + 2.303 nRT log (Hi+/Ho

+)

Divide by 2.303RT and Rearrange

log (Si+z/So

+z) = n D pH – (n+ z) F ( /DY z) Cramer & Knaff 1990, pp 19-20

Thermodynamics of H+–Linked Active TransportAntiport

If all of the free energy available in the DmH+is stored on the electrochemical potential

then we can write for Dms of solute accumulation in an antiport mechanism. Where S refers to a solute molecule and n protons to transport one solute molecule

DmH+= F DY + 2.303 RT log (Hi+/Ho

+) eq2

In antiport initial and finale states are opposite of symport so the terms in the log expression for solute are inverted:

Dms= zF + DY 2.303 RT log (So+z/Si

+z) eq3

Where i is inside and o outside; then Substituting eqs 2 & 3 into eq 1

0= zF + DY 2.303 RT log (So+z/Si

+z) + F DY + 2.303 nRT log (Hi+/Ho

+)

Rearrange and Divide by 2.303RT

log (Si+z/So

+z) = - n D pH + (n - z) F ( /DY z)Cramer & Knaff 1990, pp20-21

Lehninger 2000 Fig 12-43

SUMMARY OF TRANSPORT PROCESSES

End of Lectures