The movement of electrons through the electron carrying proteins of the inner mitochondrial membrane is shown in Figure 15.9. Also shown are inhibitors of electron movement at their point of action and the sites where artificial electron acceptors can accept electrons from the electron transport system. Specific inhibitors shown in Figure 15.9 are rotenone, amytal, antimycin A, cyanide, azide, and carbon monoxide. The artificial electron acceptors are methylene blue, phenazine methosulfate, 2,6-indophenol, tetramethyl-p-phenylene diamine, and ferricyanide.

Addition of an inhibitor to electron transport creates a crossover point - a specific target of inhibition. When an overall pathway is blocked, electron carriers will be in a reduced state behind the crossover point and in an oxidized state after it. This can easily be monitored using difference spectra and is, in fact, one of the ways in which the order of action of the electron carriers in the respiratory chain was established.

Artificial electron acceptors have the opposite effect of inhibitors. That is they relieve the build-up of electrons at a specific point arising from an inhibitor. For example, if mitochondria were treated with both antimycin A (an inhibitor) and methylene blue (an artificial electron acceptor), Complex I would be oxidized relative to CoQ, due to release of electrons from complex I to methylene blue. CoQ would remain reduced, however, because it would be blocked from transferring its electrons to the next carrier, Complex III.

See also: Difference Spectra, Rotenone, Amytal, Antimycin A, Cyanide, Azide, Carbon Monoxide, Coenzyme Q