Polyol dehydrogenases. 4. Crystallization of the l-iditol dehydrogenase of sheep liver

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Abstract
L-Iditol dehydrogenase of sheep liver, which catalyses the reversible oxidation of acyclic polyols to ketoses in the presence of DPN, has been purified and crystallized. The specific activity of the recrystallized enzyme is 350-400 times that of the original liver extract, and about 2% of the enzyme is recovered. Ultracentrifugal analysis of the recrystallized enzyme has revealed only one protein component. The optimum pH for polyol oxidation is about 10 and that for ketose reduction is about 7. Michaelis constants have been determined for xylitol, sorbitol, ribitol and DPN. Km for xylitol is about 1/6 of that for sorbitol and 1/10 of that for ribitol. The rates of oxidation of typical substrates have been compared under different conditions of pH and substrate concentration. The substrate specificity of the enzyme conforms to the rule for L-iditol dehydrogenase except for L-arabitol; however, this anomalous oxidation occurs significantly only at high substrate concentration at a high pH.