Cytochromes P450 are a group of heme-thiolate monooxygenases. They oxidize a variety of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics. an organic molecule + O2 + reduced [NADPH--hemoprotein reductase] = an alcohol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Liver. By 3-methylcholanthrene (3MC). Belongs to the cytochrome P450 family. Chimera. Its N-terminal part has been shown to be derived from what is now known as the CYP1A3. CYP1A1 has also been called CYP1A2.