A ribitol dehydrogenase (ribitol–NAD + oxidoreductase, EC. 18.104.22.168) having increased specificity and catalytic efficiency toward xylitol was isolated from mutant strains of Klebsiella aerogenes , which were selected for increased growth rate on xylitol over the ribitol dehydrogenase constitutive wild-type organism. 2. The mutant enzyme was purified to homogeneity and its general characteristics were compared with those of the previously purified wild-type enzyme. 3. Initial-velocity steady-state kinetic parameters were determined for both wild-type and mutant enzymes and the results compared. 4. The results are interpreted in terms of a model in which the mutant enzyme results from a small change of amino acid sequence, which affects both the stability and conformational equilibria of the molecule.
Ribitol dehydrogenase has been purified to homogeneity from several strains of Klebsiella aerogenes . One strain yields 3–6g of pure enzyme from 1kg of cells. The enzyme is a tetramer of four subunits, mol.wt. 27000. Preliminary studies of the activity of the enzyme are reported. Peptide ‘maps’ together with the amino acid composition indicate that the subunits are identical.