Cytochrome P450 is a heterogeneous family of isozymes whose primary function is to oxidize small molecules, both as a function of intermediary metabolism (e.g., fatty acids) and to detoxify exogenous compounds (drugs or toxins). Some isoforms have narrow substrate specificity, while others are promiscuous. The CYP1A1 isoform catalyzes 7-deethylation of ethoxyresorufin. Cytochrome P450 (CYP) plays an important role in detoxifying xenobiotics, cellular metabolism and homeostasis. One of the main mechanisms of drug-drug interactions is the induction or inhibition of these enzymes. CYP enzymes are transcriptionally activated by a variety of xenobiotics and by endogenous substrates via receptor-dependent pathways. Inhibition of these enzymes is a major factor in metabolism-based drug-drug interactions, and many chemotherapeutic medications can cause drug interactions by either inhibiting or inducing the cytochrome p450 enzyme system.

The CYP4F3B isoform catalyzes the 20-hydroxylation of leukotriene B₄.

One unit will reduce 1 nanomole of cytochrome C per minute at pH 7.4 at 37 deg C.

Solution in 100 mM potassium phosphate buffer, pH 7.4.