ID 2.7.7.69 DE GDP-L-galactose/GDP-D-glucose: hexose 1-phosphate guanylyltransferase. AN GDP-L-galactose phosphorylase. CA (1) alpha-D-mannose 1-phosphate + GDP-beta-L-galactose = beta-L-galactose CA 1-phosphate + GDP-alpha-D-mannose. CA (2) alpha-D-mannose 1-phosphate + GDP-alpha-D-glucose = alpha-D-glucose CA 1-phosphate + GDP-alpha-D-mannose. CC -!- This plant enzyme catalyzes the conversion of GDP-beta-L-galactose CC and GDP-alpha-D-glucose to beta-L-galactose 1-phosphate and alpha-D- CC glucose 1-phosphate, respectively. CC -!- The enzyme can use inorganic phosphate as the cosubstrate, CC but several hexose 1-phosphates, including alpha-D-mannose CC 1-phosphate, alpha-D-glucose 1-phosphate, and alpha-D-galactose CC 1-phosphate, are better guanylyl acceptors. CC -!- The enzyme's activity on GDP-beta-L-galactose is crucial for the CC biosynthesis of L-ascorbate. DR Q8RWE8, GGAP1_ARATH; Q9FLP9, GGAP2_ARATH; //