Catalyzes the two-step NADP-dependent conversion of GDP-4-dehydro-6-deoxy-D-mannose to GDP-fucose, involving an epimerase and a reductase reaction. GDP-beta-L-fucose + NADP(+) = GDP-4-dehydro-alpha-D-rhamnose + H(+) + NADPH Nucleotide-sugar biosynthesis; GDP-L-fucose biosynthesis via de novo pathway; GDP-L-fucose from GDP-alpha-D-mannose: step 2/2. Homodimer. Mutagen treatment of P815 tumor cells produces tum-variants that elicit a cytolytic T-lymphocyte response (CTL). The antigenic allele differs from the normal allele by a single mutation in position 139. Belongs to the NAD(P)-dependent epimerase/dehydratase family. Fucose synthase subfamily.