BIOC 212 Lecture Notes - Lecture 57: Quantum Tunnelling, Cytochrome C Oxidase, Reduction Potential
29 May 2018
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Metabolism XIX
Complex IV
• Complex IV donates electrons to oxygen
o Complex IV is a special protein complex which reduces oxygen
• The whole goal of the ETC is to take high energy electrons and remove enough
energy such that can do this safe reduction of oxygen
o Enzyme complex that catalyzed this reduction is complex IV
• Complex IV is responsible for the final step of the ETC
o Reducing O2 --> 2 H2O
o And pumping more protons!
• Accepts the lowest energy electrons coming in from cytochrome c and hands
them through another chain of heme & Fe-S cores
o Uses the ion copper in many of these centers instead of iron
• Hemes & sulfur clusters in complex IV use copper as well as iron
o Copper has stronger affinity for electrons
o Much tighter binder of electrons than iron
o Removing electrons from Cu is very difficult; this is how control the
explosiveness of adding electrons to oxygen
• This allows it to donate electrons to oxygen in a more controlled manner than
earlier redox centers in the ETC
Copper-Iron Cage Holds O2 in Place
• Geometry of this is an important component of how control redox potential of all
electrons that pass through the ETC
• As protons are pumped in, complex IV will grab other H+ from water
o Red H+ are the ones being pumped across the membrane through proton
pumps
o Other protons from water are sequentially brought into oxygen-binding sites
as electrons come in one by one to reduce O2 --> 2 H2O
o Need 4 protons & 4 electrons to react with one molecule of O2
• At the end of complex IV, get a cage or Cu & Fe hemes
o Some copper and some iron atoms
o Cage allows the electrons to be very widely shared between heme oxygen
and all redox centers around it
o Molecule of O2 comes in and binds there
• Sequentially add 4 electrons onto it, creating several highly reactive
oxygen species in the process
• ROS sequentially be quenched by hydrogens
