The enzyme, which operates in the opposite direction to that shown, forms a mixture of GDP-¦Á-D-rhamnose and its C-4 epimer, GDP-6-deoxy-¦Á-D-talose. cf. EC 1.1.1.281, GDP-4-dehydro-6-deoxy-D-mannose reductase and EC 1.1.1.135, GDP-6-deoxy-D-talose 4-dehydrogenase.