BIOC 212 Lecture Notes - Lecture 59: Nadh Dehydrogenase, Protein Structure, Conformational Change
29 May 2018
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Metabolism XXI
Protons are Exchanged during Redox Reactions
• Molecules become negatively charged as they gain an electron
• If solvent-exposed, this negative charge can be quenched by binding a proton
from water
• Loss of electrons also changes charge, allowing the loss of a proton to water or
another proton acceptor
• Chain of acid-base reactions
• In the ETC, one of the key features coupling electron transport to proton pumping
in that the temporary reduction of ETC intermediates makes them much more
attractive for a H+
o As lose that electron, lose the proton
o Sequential proton grabbing from one molecule to the next across a long
chain of side chains
• Sometimes will be moving individual protons large distances, and sometimes will
be more of an effective movement of H+ from matrix into IMS as seen before
• Passage of electrons trough one of the intermediates causes it to temporarily
accept a proton
o Subsequently lose that proton as it is re-oxidized
• When binding an electron, are making reduced electron carrier a lot more
capable of binding protons
o Much better based that in oxidized state
o Sometimes are side chains, other times are heme groups
§ Change drastically in their ability to bind electrons
• Reduced electron carrier is more basic than matrix and oxidized version is more
acidic than IMS
Direction of Flux
• How is this directionally controlled?
o Could have acid on the side where want pH to increase (equivalent to
matrix)
• And base on the other side
o Causes effective directional flow between the two in a chemical cell
• But this is not how works in biology
o Do not have chemical sink inside the IMS that brings H+ into it, since want
the protons to want to come back across membrane
o Use that energy to make ATP
o Energetically unfavorable reaction --harvest electrons to push protons
against their gradient
