A cytochrome P450 monooxygenase involved in the metabolism of various endogenous substrates, including fatty acids, steroid hormones and vitamins (PubMed:7574697, PubMed:11093772, PubMed:14559847, PubMed:15766564, PubMed:19965576). Mechanistically, uses molecular oxygen inserting one oxygen atom into a substrate, and reducing the second into a water molecule, with two electrons provided by NADPH via cytochrome P450 reductase (NADPH--hemoprotein reductase) (PubMed:7574697, PubMed:11093772, PubMed:14559847, PubMed:15766564, PubMed:19965576). Primarily catalyzes the epoxidation of double bonds of polyunsaturated fatty acids (PUFA) with a preference for the last double bond (PubMed:7574697, PubMed:15766564, PubMed:19965576). Catalyzes the hydroxylation of carbon-hydrogen bonds. Metabolizes all trans-retinoic acid toward its 4-hydroxylated form (PubMed:11093772). Displays 16-alpha hydroxylase activity toward estrogen steroid hormones, 17beta-estradiol (E2) and estrone (E1) (PubMed:14559847). Plays a role in the oxidative metabolism of xenobiotics. It is the principal enzyme responsible for the metabolism of the anti-cancer drug paclitaxel (taxol) (PubMed:26427316).

[Isoform 1]: UDP-glucuronosyltransferase (UGT) that catalyzes phase II biotransformation reactions in which lipophilic substrates are conjugated with glucuronic acid to increase the metabolite's water solubility, thereby facilitating excretion into either the urine or bile (PubMed:15472229, PubMed:18674515, PubMed:18719240, PubMed:23756265, PubMed:23288867, PubMed:24641623). Essential for the elimination and detoxification of drugs, xenobiotics and endogenous compounds (PubMed:23756265). Catalyzes the glucuronidation of endogenous estrogen hormones such as estradiol and estrone (PubMed:15472229, PubMed:18719240, PubMed:23288867). Contributes to bile acid (BA) detoxification by catalyzing the glucuronidation of BA substrates, which are natural detergents for dietary lipids absorption (PubMed:23756265). Involved in the glucuronidation of calcidiol, which is the major circulating form of vitamin D3, essential for the regulation of calcium and phosphate homeostasis (PubMed:24641623). Involved in the glucuronidation of the AGTR1 angiotensin receptor antagonists losartan, candesartan and zolarsartan, which can inhibit the effect of angiotensin II (PubMed:18674515).

UDP-glucuronosyltransferase (UGT) that catalyzes phase II biotransformation reactions in which lipophilic substrates are conjugated with glucuronic acid to increase the metabolite's water solubility, thereby facilitating excretion into either the urine or bile (PubMed:10702251, PubMed:15472229, PubMed:15470161, PubMed:18674515, PubMed:18719240, PubMed:19022937, PubMed:23288867, PubMed:23756265, PubMed:26220143, PubMed:17442341). Essential for the elimination and detoxification of drugs, xenobiotics and endogenous compounds (PubMed:15470161, PubMed:18674515, PubMed:23756265). Catalyzes the glucuronidation of endogenous steroid hormones such as androgens (epitestosterone, androsterone) and estrogens (estradiol, epiestradiol, estriol, catechol estrogens) (PubMed:2159463, PubMed:15472229, PubMed:18719240, PubMed:19022937, PubMed:23288867, PubMed:26220143, PubMed:17442341). Also regulates the levels of retinoic acid, a major metabolite of vitamin A involved in apoptosis, cellular growth and differentiation, and embryonic development (PubMed:10702251). Contributes to bile acid (BA) detoxification by catalyzing the glucuronidation of BA substrates, which are natural detergents for dietary lipids absorption (PubMed:23756265). Involved in the glucuronidation of the AGTR1 angiotensin receptor antagonist losartan, caderastan and zolarsatan, drugs which can inhibit the effect of angiotensin II (PubMed:18674515). Also metabolizes mycophenolate, an immunosuppressive agent (PubMed:15470161).