d-Fucose Metabolism in a Pseudomonad
I. OXIDATION OF d-FUCOSE TO d-FUCONO-
-LACTONE BY A d-ALDOHEXOSE DEHYDROGENASE
A. Stephen Dahms 1 and Richard L. Anderson 1
From the
1 From the Department of Biochemistry, Michigan State University, East Lansing, Michigan 48823
A soluble, NAD-dependent dehydrogenase which is specific for d-aldohexoses, including d-fucose, d-glucose, d-galactose, d-mannose, d-altrose, d-allose, 2-deoxy-d-glucose, and 2-deoxy-d-galactose, has been purified 335-fold from a pseudomonad capable of using d-fucose as a sole carbon source. Forty-five other sugars and related compounds tested did not serve as substrates and did not affect the rate of d-glucose oxidation. The pH optimum was 8 to 8.5 in Tris-HCl buffer and 9 to 10 in glycine-NaOH buffer. The enzyme was insensitive to thiols and thiol group reagents and was not activated by divalent metal ions. Representative apparent Km values were 5.8 mm for d-fucose, 0.86 mm for d-glucose and 0.08 mm for NAD+. The ß anomer of d-glucose was preferred over the 
anomer. d-Fuconate was isolated as the apparent product of d-fucose oxidation, indicating that the unstable d-fucono--lactone rather than d-fucono-
-lactone was the immediate product. This was confirmed by the demonstration that d-glucono--lactone, but not d-fucono--lactone or d-galactono--lactone, could serve as a substrate in the reverse reaction. Thus, it is concluded that ß-d-glucopyranose and ß-d-fucopyranose are the actual substrates for the enzyme.
Submitted on November 19, 1971
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