Fig. 2.

Schematic representation of subunits of mitochondrial oxidative phosphorylation complexes. Hydrogen ions are transported from the mitochondrial matrix across the inner mitochondrial membrane into the intermembrane space by complexes I, III, and IV. The movement of hydrogen ions down the electrochemical gradient is coupled to the phosphorylation of adenosine diphosphate (ADP) to form adenosine triphosphate (ATP) by complex V. Electrons from the autofluorescent reducing agent, nicotine adenine dinucleotide (NADH), move from complex I through ubiquinone to complex III and then complex IV via cytochrome c (Cyt c). Electrons from succinate, another reducing agent, enter the respiratory chain through flavin adenine dinucleotide (FAD), which is covalently linked to complex II of the respiratory chain. Like NADH, the reduced form of FAD (FADH) is autofluorescent. Rotenone (ROT) and potassium cyanide (KCN) inhibit complex I and IV, respectively. Pentachlorophenol (PCP) is a protonophore which increases membrane proton conductivity, disrupts the proton gradient across the membrane, and as a result uncouples mitochondrial electron transport chain from phosphorylation.