ID 5.1.3.18 DE GDP-mannose 3,5-epimerase. CA (1) GDP-alpha-D-mannose = GDP-beta-L-gulose. CA (2) GDP-beta-L-gulose = GDP-beta-L-galactose. CC -!- The enzyme catalyze the formation of the stable intermediate GDP- CC beta-L-gulose as well as GDP-beta-L-galactose. CC -!- The reaction proceeds by C4' oxidation of GDP-alpha-D-mannose CC followed by epimerization of the C5' position to give GDP-beta-L-4- CC dehydro-gulose. CC -!- This intermediate is either reduced to give GDP-beta-L-gulose or the CC C3' position is epimerized to give GDP-beta-L-4-dehydro-galactose, CC followed by C4' reduction to yield GDP-beta-L-galactose. CC -!- Both products serve as intermediates in two different variants of CC plant L-ascorbate biosynthesis pathways. DR A2Z7B3, GME1_ORYSI ; A3C4S4, GME1_ORYSJ ; Q2R1V8, GME2_ORYSJ ; DR Q93VR3, GME_ARATH ; //