l-Fucose, 6-deoxy-l-galactose, is a key component of many important glycoconjugates including the blood group antigens and the LewisX ligands. The biosynthesis of GDP-l- fucose begins with the action of a dehydratase that converts GDP-d-mannose into GDP-4- keto-6-deoxy-mannose. The enzyme GDP-fucose synthase, GFS,(also known as GDP-4- keto-6-deoxy-d-mannose epimerase/reductase, GMER) then converts GDP-4-keto-6- ...