Bifunctional enzyme involved in dTDP-beta-L-rhamnose biosynthesis. Catalyzes the epimerization of the C3' and C5'positions of dTDP-6-deoxy-4-keto-alpha-D-glucose to form dTDP-4-keto-beta-L-rhamnose and its reduction to yield dTDP-beta-L-rhamnose. Can form UDP-beta-L-rhamnose from UDP-6-deoxy-4-keto-alpha-D-glucose, but cannot convert GDP-4-dehydro-6-deoxy-D-mannose to GDP-fucose. dTDP-4-dehydro-6-deoxy-alpha-D-glucose = dTDP-4-dehydro-beta-L-rhamnose dTDP-beta-L-rhamnose + NADP(+) = dTDP-4-dehydro-beta-L-rhamnose + H(+) + NADPH Optimum pH is 5.5-7.5. Optimum temperature is 30 degrees Celsius. Carbohydrate biosynthesis; dTDP-L-rhamnose biosynthesis. Expressed in roots, leaves, stems and flowers. Belongs to the dTDP-4-dehydrorhamnose reductase family.