2.7.7.69	GDP-alpha-D-glucose + alpha-D-mannose 1-phosphate	-	
2.7.7.69	GDP-beta-L-galactose + alpha-D-mannose 1-phosphate	-	
2.7.7.69	GDP-beta-L-galactose + phosphate	enzyme guanylylates a conserved active site His residue with GDP-L-galactose, forming L-galactose 1-phosphate for vitamin C synthesis, and regeneration of the enzyme with phosphate to form GDP