Cloning,Purification and Characterization of an NAD-Dependent <Emphasis Type="SmallCaps">d</Emphasis>-Arabitol Dehydrogenase from Acetic Acid Bacterium, <Emphasis Type="Italic">Acetobacter suboxydans</Emphasis>

d-Xylulose-forming d-arabitol dehydrogenase (aArDH) is a key enzyme in the bio-conversion of d-arabitol to xylitol. In this study, we cloned the NAD-dependent d-xylulose-forming d-arabitol dehydrogenase gene from an acetic acid bacterium, Acetobacter suboxydans sp. The enzyme was purified from A. suboxydans sp. and was heterogeneously expressed in Escherichia coli. The native or recombinant enzyme was preferred NAD(H) to NADP(H) as coenzyme. The active recombinant aArDH expressed in E. coli is a homodimer, whereas the native aArDH in A. suboxydans is a homotetramer. On SDS–PAGE, the recombinant and native aArDH give one protein band at the position corresponding to 28 kDa. The optimum pH of polyol oxidation and ketone reduction is found to be pH 8.5 and 5.5 respectively. The highest reaction rate is observed when d-arabitol is used as the substrate (K _m = 4.5 mM) and the product is determined to be d-xylulose by HPLC analysis.