Reaction: (1) GDP-α-D-mannose = GDP-β-L-galactose
(2) GDP-α-D-mannose = GDP-β-L-gulose
Other name(s): GME (gene name); GDP-D-mannose:GDP-L-galactose epimerase; guanosine 5'-diphosphate D-mannose:guanosine 5'-diphosphate L-galactose epimerase
Systematic name: GDP-α-D-mannose 3,5-epimerase
Comments: The enzyme catalyses the formation of the stable intermediate GDP-β-L-gulose as well as GDP-β-L-galactose. The reaction proceeds by C4' oxidation of GDP-α-D-mannose followed by epimerization of the C5' position to give GDP-β-L-4-dehydro-gulose. This intermediate is either reduced to give GDP-β-L-gulose or the C3' position is epimerized to give GDP-β-L-4-dehydro-galactose, followed by C4' reduction to yield GDP-β-L-galactose. Both products serve as intermediates in two different variants of plant L-ascorbate biosynthesis pathways.
Links to other databases: BRENDA, EXPASY, GTD, KEGG, MetaCyc, PDB, CAS registry number: 72162-82-4
References:
1. Hebda, P.A., Behrman, E.J. and Barber, G.A. The guanosine 5'-diphosphate D-mannose: guanosine 5'-diphosphate L-galactose epimerase of Chlorella pyrenoidosa. Chemical synthesis of guanosine 5'-diphosphate L-galactose and further studies of the enzyme and the reaction it catalyzes. Arch. Biochem. Biophys. 194 (1979) 496-502. [PMID: 443816]
2. Barber, G.A. and Hebda, P.A. GDP-D-mannose: GDP-L-galactose epimerase from Chlorella pyrenoidosa. Methods Enzymol. 83 (1982) 522-525. [PMID: 7098948]
3. Wolucka, B.A., Persiau, G., Van Doorsselaere, J., Davey, M.W., Demol, H., Vandekerckhove, J., Van Montagu, M., Zabeau, M. and Boerjan, W. Partial purification and identification of GDP-mannose 3",5"-epimerase of Arabidopsis thaliana, a key enzyme of the plant vitamin C pathway. Proc. Natl. Acad. Sci. USA 98 (2001) 14843-14848. [PMID: 11752432]
4. Major, L.L., Wolucka, B.A. and Naismith, J.H. Structure and function of GDP-mannose-3',5'-epimerase: an enzyme which performs three chemical reactions at the same active site. J. Am. Chem. Soc. 127 (2005) 18309-18320. [PMID: 16366586]
5. Watanabe, K., Suzuki, K. and Kitamura, S. Characterization of a GDP-D-mannose 3'',5''-epimerase from rice. Phytochemistry 67 (2006) 338-346. [PMID: 16413588]