General term for a group of heme-containing monooxygenases (EC 1.4.14.1). Named from the prominent absorption band of the Fe(II)-carbonyl complex. The heme comprises protophorphyrin IX, and the proximal ligand to iron is a cysteine sulfur. Cytochromes P-450 of microsomes in tissues such as liver are responsible for metabolism of many xenobiotics, including drugs. Others, such as the mitochondrial enzymes from adrenal glands, are involved in biosynthetic pathways such as those of steroids. The reaction with dioxygen appears to involve higher oxidation states of iron, such as Fe(IV)=O.
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