Chemiosmotic Theory

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Chemiosmotic Theory
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The Chemiosmotic theory can explain several key
observations
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1. Inhibit e- transport Inhibit ATP
synthesis
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2. Inhibit ATP synthesis- inhibit the ETC

• Oligomycin Inhibitor of ATP Synthase

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3.Intact mitochondria that has been disrupted
with detergents

• Can catalyze e- transport but there will be no
  ATP synthesis as a H gradient can not be
  maintained

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4. Chemical Uncouplers

• Weak, hydrophobic acids
• They can pick up H from the inter membrane
  space
• thereby becoming protonated
• the protonated acids readily diffuse across the
  membrane
• and release the H into the matrix
• This dissipates the H gradient

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Uncouplers
2,4-DNP
H

• e- transport and oxygen consumption continues
• There is however no ATP synthesis

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5. Ionophores

• e.g. Valinomycin- specific for K
• Also uncouples e- transport from ATP synthesis by
  allowing inorganic ions to readily pass through
  the inner mitochondrial membrane.
• This dissipates the electrical component of the
  proton motive force (major component)

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Physiological uncouplers- THERMOGENIN

• Found in Brown Adipose tissue in hibernating
  animals and neonates
• Helps generate heat
• BAT contains a large number of mitochondria

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Testing the chemiosmotic Hypothesis

• Efraim Racker and Walther Stoeckenius

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Adenine Nucleotide and Phosphate Translocase

• Both these transport processes are driven by the
  proton motive force are

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Acceptor Control Ratio

• Oxid. Phosphorylation is driven by the
  concentration of ADP
• Relates to the function of Ox PhosATP synthesis
• When ATP is utilized..ADP and Pi increases
• Called Acceptor control or Respiratory
  Control

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Stoichiometry of O2 consumption and ATP synthesis

• Given by the P/O ratio.. Moles of ATP formed per
  mole of oxygen reduced (1/2 O2 reduced)
• Per mole of NADH oxidized.2-3 moles of ATP is
  synthesized
• Per mole of FADH2.1-2 moles of ATP is
  synthesized
• Oxidation of either NADH or FADH2 reduces ½ O2 to
  H2O
• Therfore the P/O ratio for NADH and FADH2 are
  2.5 and 1.5

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• Most studies show that 4 H are required to drive
  the synthesis of 1 ATP
• 10 H are pumped per mole of NADH oxidized
• Therefore oxidation of NADH can produce
• 10/4 2.5 moles of ATP (P/O 2.5)
• For FADH2 6/4 1.5 (P/O 1.5)