Adrenodoxin is a small iron-sulfur protein that can accept and carry a single electron.

Adrenodoxin functions as an electron transfer protein in the mitochondrial cytochrome P450 systems.

FAD can be reduced by two electrons donated from coenzyme NADPH.

[7] This particular oxidation/reduction system is involved in the synthesis of steroid hormones in steroidogenic tissues.

In addition, similar systems also function in vitamin D and bile acid synthesis in the kidney and liver respectively.