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Information on EC - GDP-4-dehydro-6-deoxy-alpha-D-mannose 3-dehydratase

for references in articles please use BRENDA:EC4.2.1.168
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EC Tree
     4 Lyases
         4.2 Carbon-oxygen lyases
             4.2.1 Hydro-lyases
       GDP-4-dehydro-6-deoxy-alpha-D-mannose 3-dehydratase
IUBMB Comments
This enzyme, involved in beta-L-colitose biosynthesis, is a unique vitamin-B6-dependent enzyme. In the first step of catalysis, the bound pyridoxal phosphate (PLP) cafactor is transaminated to the pyridoxamine 5'-phosphate (PMP) form of vitamin B6, using L-glutamate as the amino group donor. The PMP cofactor then forms a Schiff base with the sugar substrate and the resulting adduct undergoes a 1,4-dehydration to eliminate the 3-OH group. Hydrolysis of the product from the enzyme restores the PLP cofactor and results in the release of an unstable enamine intermediate. This intermediate tautomerizes to form an imine form, which hydrolyses spontaneously, releasing ammonia and forming the final product.
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The expected taxonomic range for this enzyme is: Bacteria, Eukaryota
colD, GDP-4-keto-6-deoxy-D-mannose-3-dehydratase, WbdK, more
2-GDP-[(2S,3S,6R)-5-amino-6-methyl-3,6-dihydro-2H-pyran-3-ol] = 2-GDP-[(2S,3S,6R)-5-imino-6-methyloxan-3-ol]
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(1b), spontaneous
GDP-2-[(2S,3S,6R)-5-imino-6-methyloxan-3-ol] + H2O = GDP-4-dehydro-3,6-dideoxy-alpha-D-mannose + NH3
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(1c), spontaneous
GDP-4-dehydro-alpha-D-rhamnose + L-glutamate = 2-GDP-[(2S,3S,6R)-5-amino-6-methyl-3,6-dihydro-2H-pyran-3-ol] + 2-oxoglutarate + H2O
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GDP-4-dehydro-alpha-D-rhamnose + L-glutamate = GDP-4-dehydro-3,6-dideoxy-alpha-D-mannose + 2-oxoglutarate + NH3
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overall reaction
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