Amnuay Thithapandhaอำนวย ฐิตาพันธ์Mahidol University. Faculty of Medicine Ramathibodi Hospital. Office of Academic Affairs2022-10-112022-10-112022-10-112009Ramathibodi Medical Journal. Vol. 32, No. 2 (Apr-Jun 2009), 101-1040125-3611 (Print)2651-0561 (Online)https://repository.li.mahidol.ac.th/handle/123456789/79892Cytochrome P450s or CYPs are heme proteins found in several organs but in high amount in both mammalian and human livers. The heme iron binds oxygen in the CYP active site, where oxidation of xenobiotics and endogenous compounds occurs. Electrons are supplied by the enzyme NADPH-cyto- chrome P450 oxidoreductase and its cofactor, NADPH. Metabolism of a substrate by a CYP consumes one molecule of O2 and produces on oxidized substrate and a molecule of water (Fig. 1). Depending on the nature of the substrate, the reaction for some CYPs is partially “uncoupled,” consuming more Oz than substrate metabolized and producing “activated oxygen” or O2 which is usually converted to water by the enzyme superoxide dismutase (SOD).engCytochromeArticleOffice of Academic Affairs Faculty of Medicine Ramathibodi Hospital Mahidol University