The function of ENSG00000241635 (UGT1A1, UDP glucuronosyltransferase family 1 member A1) 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:12181437, PubMed:15472229, PubMed:18004206, PubMed:18004212, PubMed:18719240, PubMed:19830808, PubMed:23288867, PubMed:15231852, PubMed:21422672, PubMed:38211441). Essential for the elimination and detoxification of drugs, xenobiotics and endogenous compounds (PubMed:12181437, PubMed:18004206, PubMed:18004212). Catalyzes the glucuronidation of endogenous estrogen hormones such as estradiol, estrone and estriol (PubMed:15472229, PubMed:18719240, PubMed:23288867). Involved in the glucuronidation of bilirubin, a degradation product occurring in the normal catabolic pathway that breaks down heme in vertebrates (PubMed:17187418, PubMed:18004206, PubMed:19830808, PubMed:24525562). Involved in the glucuronidation of arachidonic acid (AA) and AA-derived eicosanoids including 15-HETE, 20- HETE, PGB1 and F2-isoprostane (8-iso-PGF2alpha) (PubMed:15231852, PubMed:38211441). Involved in the glucuronidation of the phytochemical ferulic acid at the phenolic or the carboxylic acid group (PubMed:21422672). Also catalyzes the glucuronidation the isoflavones genistein, daidzein, glycitein, formononetin, biochanin A and prunetin, which are phytoestrogens with anticancer and cardiovascular properties (PubMed:18052087, PubMed:19545173). Involved in the glucuronidation of the AGTR1 angiotensin receptor antagonist losartan, a drug which can inhibit the effect of angiotensin II (PubMed:18674515). Involved in the biotransformation of 7-ethyl-10-hydroxycamptothecin (SN-38), the pharmacologically active metabolite of the anticancer drug irinotecan (PubMed:12181437, PubMed:18004212, PubMed:20610558). {ECO:0000269|PubMed:12181437, ECO:0000269|PubMed:15231852, ECO:0000269|PubMed:15472229, ECO:0000269|PubMed:17187418, ECO:0000269|PubMed:18004206, ECO:0000269|PubMed:18004212, ECO:0000269|PubMed:18052087, ECO:0000269|PubMed:18674515, ECO:0000269|PubMed:18719240, ECO:0000269|PubMed:19545173, ECO:0000269|PubMed:19830808, ECO:0000269|PubMed:20610558, ECO:0000269|PubMed:21422672, ECO:0000269|PubMed:23288867, ECO:0000269|PubMed:24525562, ECO:0000269|PubMed:38211441}. [Isoform 2]: Lacks UGT glucuronidation activity but acts as a negative regulator of isoform 1. {ECO:0000269|PubMed:17187418, ECO:0000269|PubMed:18004212, ECO:0000269|PubMed:20610558}.