Reaction Mechanism and Regioselectivity of Uridine Diphosphate Glucosyltransferase RrUGT3Mengsha Li & Cai You & Fei Guo & Qingfang Han & Xixian Xie & Lijuan Ma & Shengying Li & Lei Du & Xiang Sheng & Hao SuPDF3.1 MBEN