Member of a superfamily of heme-containing monooxygenases involved in xenobiotic metabolism, cholesterol biosynthesis, and steroidogenesis, in eukaryotic organisms found mainly in the endoplasmic reticulum and inner mitochondrial membrane of cells. ‘P450’ refers to a feature in the carbon monoxide absorption difference spectrum at 450 nm caused by the presence of a thiolate in the axial position of the heme opposite to the carbon monoxide ligand.