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. Essential for the elimination and detoxification of drugs, xenobiotics and endogenous compounds. Catalyzes the glucuronidation of endogenous estrogen hormones such as estradiol and estrone. Contributes to bile acid (BA) detoxification by catalyzing the glucuronidation of BA substrates, which are natural detergents for dietary lipids absorption. Involved in the glucuronidation of calcidiol, which is the major circulating form of vitamin D3, essential for the regulation of calcium and phosphate homeostasis. Involved in the glucuronidation of the AGTR1 angiotensin receptor antagonists losartan, candesartan and zolarsartan, which can inhibit the effect of angiotensin II. glucuronate acceptor + UDP-alpha-D-glucuronate = acceptor beta-D-glucuronoside + H(+) + UDP 17beta-estradiol + UDP-alpha-D-glucuronate = 17beta-estradiol 3-O-(beta-D-glucuronate) + H(+) + UDP 17beta-estradiol + UDP-alpha-D-glucuronate = 17beta-estradiol 17-O-(beta-D-glucuronate) + H(+) + UDP 17alpha-estradiol + UDP-alpha-D-glucuronate = 17alpha-estradiol 3-O-(beta-D-glucuronate) + H(+) + UDP estrone + UDP-alpha-D-glucuronate = estrone 3-O-(beta-D-glucuronate) + H(+) + UDP chenodeoxycholate + UDP-alpha-D-glucuronate = chenodeoxycholoyl-24-O-(beta-D-glucuronate) + UDP deoxycholate + UDP-alpha-D-glucuronate = deoxycholoyl-24-O-(beta-D-glucuronate) + UDP lithocholate + UDP-alpha-D-glucuronate = lithocholoyl-24-O-(beta-D-glucuronate) + UDP hyodeoxycholate + UDP-alpha-D-glucuronate = hyodeoxycholoyl-24-O-(beta-D-glucuronate) + UDP hyocholate + UDP-alpha-D-glucuronate = hyocholoyl-24-O-(beta-D-glucuronate) + UDP calcidiol + UDP-alpha-D-glucuronate = calcidiol 25-O-(beta-D-glucuronide) + H(+) + UDP losartan + UDP-alpha-D-glucuronate = losartan-2-N-beta-D-glucuronide + UDP candesartan + UDP-alpha-D-glucuronate = candesartan-2-N-beta-D-glucuronide + UDP UDP-alpha-D-glucuronate + zolasartan = UDP + zolarsartan-2-N-beta-D-glucuronide Homodimers. Homooligomer. Interacts with UGT1A1, UGT1A4, UGT1A6, UGT1A7, UGT1A8, UGT1A9 and UGT1A10 to form heterodimers. UGT1A3 is one of the isoforms produced at the UGT1A complex locus. The UGT1A complex locus produces different isoforms based on alternative use of promoters, first exons and terminal exons. Belongs to the UDP-glycosyltransferase family.