The function of ENSG00000288702 (UGT1A3, UDP glucuronosyltransferase family 1 member A3) is as follows. [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:23288867, PubMed:23756265, PubMed:24641623, PubMed:21422672). 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 phytochemical ferulic acid at the phenolic or the carboxylic acid group (PubMed:21422672). Involved in the glucuronidation of the AGTR1 angiotensin receptor antagonists losartan, candesartan and zolarsartan, which can inhibit the effect of angiotensin II (PubMed:18674515). {ECO:0000269|PubMed:15472229, ECO:0000269|PubMed:18674515, ECO:0000269|PubMed:18719240, ECO:0000269|PubMed:21422672, ECO:0000269|PubMed:23288867, ECO:0000269|PubMed:23756265, ECO:0000269|PubMed:24641623}. [Isoform 2]: Lacks UDP-glucuronosyltransferase (UGT) activity but acts as a negative regulator of isoform 1. .