GDP-L-Fucose Synthase is a NADP(H)-binding protein. It catalyzes the two-step epimerase and the reductase reactions in GDP-D-mannose metabolism, converting GDP-4-keto-6-D-dexoymannose to GDP-L-fucose. GDP-L-Fucose is the substrate of several fucosyltransferase, involving the expression of mamy glycoconjugates, including blood group ABH antigens and development adhesion antigens. Mutations in the TSTA3 gene may cause leukocyte adhesion deficiency type II.