Overview of the Pathway

Oxidation-Reduction Reactions

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.

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.