Purification and properties of Bacillus subtilis inositol dehydrogenase

Inositol 2-dehydrogenase (EC 1.1.1.18) activity appears during growth of Bacillus subtilis (strain 60015) in nutrient sporulation medium. Its synthesis is induced by myo-inositol and repressed by D-glucose. The enzyme has an apparent molecular weight of 155,000 to 160,000 as determined by sucrose density gradient centrifugation, and it is comprised of four subunits, each having a molecular weight of 39,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isoelectric point of the enzyme is 4.4 as determined by column isoelectric focusing. The enzyme shows the highest Vmax and lowest Km with myo-inositol as substrate but does not react with scyllo-inositol; it also reacts with the alpha anomer (but not the beta anomer) of D-glucose and with D-xylose. Apparently, the enzyme can remove only the single equatorial hydrogen of the cyclitol or pyranose ring. In contrast to the glucose dehydrogenase of spores, which reacts with D-glucose or 2-deoxy-D-glucose and with NAD or NADP, inositol dehydrogenase requires NAD and does not react with 2-deoxy-D-glucose.