Distribution of myo-inositol dehydrogenase in algae

The enzyme myo-inositol dehydrogenase (InDH; EC 1.1.1.18) catalyses the NAD-dependent oxidation of myo-inositol to scyllo-inosose (2-keto-inositol). A survey within different algal groups showed that this enzyme is present in rhodophytes, glaucocystophytes, phaeophytes, xanthophytes and haptophytes but not in green algae, euglenophytes and chrysophytes. Anion-exchange chromatography of crude homogenates resulted in two distinct peaks of activity. Both isoenzymes were specific for myo-inositol and scyllo-inosose. epi- and scyllo-inositol as well as epi-inosose were only poor substrates, while all other polyols and sugars tested did not serve as substrates. A possible role of the InDH isoenzymes is the shuttling of reducing power between the mitochondrion and the cytosol.