In general, Cytochrome P450 (CYP) genes are divided into two groups: CYP1 and CYP2 families. The members of both gene clusters share a highly conserved structural organization consisting of 3 domains; Cytochrome P450 proteins contain approximately 440 amino acids that form an internal cavity binding site for oxygen or other reducing equivalents (Source). Cytochromes P-450 perform their catalytic function associated with NADPH-dependent reductase while metabolizing drugs/xenobiotics through transferases reaction involving two electrons.

Cytochrome P450 (CYP) part of phase I detoxification in the liver. Cytochrome P450 (CYP) enzymes are membrane-bound hemoproteins that play an essential role in detoxifying xenobiotics, cellular metabolism, and homeostasis. Cytochrome P450 is one of the most important classes of enzymes involved in drug metabolism. It is estimated that more than 60% of current drugs undergo metabolism by Cytochrome P450 enzymes. Cytochrome P450 enzymes are found in the liver, small intestine, and other tissues of the body.

CYP1B1: The CYP1B1 gene encodes a member of the cytochrome P450 family of enzymes. CYP1B1 is involved in metabolizing lipids, fats, cholesterol, and steroid hormones. SNPs in the CYP1B1 gene predict risk of hormone dependent diseases and efficacy of treatments of such diseases. The enzyme encoded by this gene localizes to the endoplasmic reticulum and metabolizes procarcinogens such as polycyclic aromatic hydrocarbons and 17beta-estradiol which is a steroid.

Of all the Cytochrome P450 enzymes, the CYP1B1 enzyme has the highest estrogen expression and hydroxylation in breast tissue. CYP1B1 metabolizes estradiol (or E2) to form 4-OH-estradiol and other metabolites. 4-OH-estradiol, which is pro-carcinogenic, has been shown to induce carcinomas. Changes in the CYP1B1 gene sequence regarding SNPs can potentially change the activity of the CYP1B1 enzyme and increase the amount of 4-OH-estradiol, which may also have implications for lifetime cancer risk.