Fig. 6.
Electron transport to mitochondrial forms of cytochrome P450. The flavin group (FAD) of ferredoxin reductase (FeRed), which is bound to the IMM, accepts two electrons from NADPH, converting it to NADP+. These electrons pass to the iron-sulfur (Fe2S2, diamond with dots) cluster of ferredoxin (Fedx), which is found either in the mitochondrial matrix, as shown, or loosely associated with the IMM. Fedx then donates the electrons to the heme of the P450 (square with Fe). Negatively charged residues in Fedx (−) guide docking and electron transfer with positively charged residues (+) in both FeRed and the P450. For P450scc, three pairs of electrons must be transported to the P450 to convert cholesterol to pregnenolone. [© W. L. Miller.]