L-Gulose is a very rare sugar, but appears as a sugar component of the main polar lipids characteristic in such a thermophilic archaeon as Thermoplasma acidophilum that lives without cell walls in a highly acidic environment. The biosynthesis of L-gulose in this thermophilic organism was investigated with deuterium- labeling experiments. L-Gulose was found to be biosynthesized from D-glucose via stepwise stereochemical inversion at C-2 and C-5. The involvement of an epimerase related to GDP-mannose 3,5-epimerase, the key enzyme of plant ascorbate biosynthesis, was also suggested in this C-5 inversion. The resemblance of Lgulose biosynthesis in archaea and plants might be suggested from these results.
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