Catalyzes the two-electron reduction of urocanate to dihydrourocanate (also named imidazole propionate or deamino-histidine). Dihydrourocanate is present at higher concentrations in subjects with type 2 diabetes, and directly impairs glucose tolerance and insulin signaling at the level of insulin receptor substrate (IRS) through activation of p38 gamma (MAPK12)-p62-mTORC1. Therefore, the UrdA enzyme from the gut bacteria S.mutans strain UA159 may contribute to the pathogenesis of type 2 diabetes by producing the microbial metabolite dihydrourocanate. A + dihydrourocanate = AH2 + urocanate Binds 1 FAD per subunit. Binds 1 FMN covalently per subunit. S.mutans strain UA159 is significantly more abundant in subjects with type 2 diabetes (T2D) compared with subjects with normal glucose tolerance (NGT). Belongs to the FAD-dependent oxidoreductase 2 family. FRD/SDH subfamily.