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The following blue boxes represent the oxidation-reduction reactions that are occuring in each
respective complex. Everything within the blue box are those compounds or sites which are
tightly bound, constitutive parts of the enzyme. Compounds outside the blue box are
mobile electron (ie. hydride ion) carriers.
The following abbreviations are also used below; FMN - Flavin mononucleotide, Fe2+S -
reduced iron-sulfur center, Fe3+S - oxidized iron-sulfur center, cyt - cytochrome,
CoQ - Coenzyme Q.
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Chemistry of Complex V
Complexes I, II, and IV all "pump" protons (ie. H+) into the mitochondrial space
between the inner and outer mitochondrial membrane, establishing a proton gradient across the
inner mitochondrial membrane. As the protons pass through Complex V, the osmotic energy
of the gradient is converted into chemical energy, in the form of ATP. The use of this
transmembrane proton gradient, created by the exergonic reduction reactions
occuring between Complex I and Complex IV, to
drive the endergonic reaction of ATP synthesis is known as chemiosmotic coupling.
Chemiosmotic coupling is acheived through the unique structure of Complex V. As seen in the
schematic image, Complex V is composed of an F1 and an F0 particle.
The F1 particle consists of a knob-like structure, which is attached
to stalk proteins, linked to the F0 base. The F1 has multiple subunits,
three alpha, three beta, one gamma, one delta, and one epsilon. The site of ATP synthesis is the
beta subunit.
Recent research conducted by Paul Boyer
and John Walker
has elucidated the conformational mechanism that occurs during ATP synthesis, awarding them
the 1997 Noble Prize in Chemistry. The press release from the Royal Swedish Academy of Sciences
explains how the enzyme functions as a type of micro-rotary engine, in which periodic
conformational changes occur in the beta subunits of the F1 knob.
Unfortunately, although the Nobel Prize committee awarded Boyer and Walker for "their elucidation
of the enzymatic mechanism underlying the synthesis of ATP," neither researcher gave any
chemical mechanism by which ATP is synthesized in the enzyme. However, a still unrecognized,
independent research team did propose a chemical mechanism for ATP synthesis,
known as the pseudorotation mechanism.
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