D-glucosaminate dehydratase from Agrobacterium radiobacter. Physicochemical and enzymological properties

The bacterial distribution of D-glucosaminate dehydratase [EC 4.2.1.26] was investigated and Agrobacterium radiobacter (IAM 1526) was found to have the highest enzyme activity. The enzyme was formed inducibly in a glycerol-urea medium by D-glucosamine, D-galactosamine, and D-glucosamine, but not by D-mannosamine. The enzyme purified from the cells grown in the glucosamine-glycerol-urea medium was shown to be homogeneous by ultracentrifugation. The molecular weight was determined to be about 66,000 by the sedimentation equilibrium method, and 72,800 by the gel permeation chromatography low-angle light scattering method. The pH optimum is 8.3-9.0. The enzyme catalyzed the dehydration of D-glucosaminate (relative activity: 100, Km: 2.8 mM), D-galactosaminate (31.5, 5.0 mM), D-mannosaminate (17.5, 29 mM), D-threonine (5.1, 4.8 mM), D-serine (3.2, 0.026 mM), and L-serine (1.1, ND), but not L-threonine. The reverse reaction does not occur. The enzyme is inhibited by typical inhibitors of pyridoxal 5'-phosphate enzymes, such as L'penicillamine, and also by carbonyl reagents, thiol reagents, divalent metals, and several D-amino acids and D-amino sugars.