Characterization of a recombinant l-fucose isomerase from Caldicellulosiruptor saccharolyticus that isomerizes l-fucose, d-arabinose, d-altrose, and l-galactose
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A recombinant l-fucose isomerase from Caldicellulosiruptor saccharolyticus was purified as a single 68 kDa band with an activity of 76 U mg−1. The molecular mass of the native enzyme was 204 kDa as a trimer. The maximum activity for l-fucose isomerization was at pH 7 and 75°C in the presence of 1 mM Mn2+. Its half-life at 70°C was 6.1 h. For aldose substrates, the enzyme displayed activity in decreasing order for l-fucose, with a kcat of 11,910 min−1 and a Km of 140 mM, d-arabinose, d-altrose, and l-galactose. These aldoses were converted to the ketoses l-fuculose, d-ribulose, d-psicose, and l-tagatose, respectively, with 24, 24, 85, 55% conversion yields after 3 h.