MYOINOSITOL DEHYDROGENASE FROM THE ACIDOPHILIC AND THERMOPHILIC RED ALGA GALDIERIA-SULPHURARIA

A NAD-dependent myo-inositol dehydrogenase (EC 1.1.1.18) has been puri fied from the acido- and thermophilic red alga Galdieria sulphuraria. This enzyme catalyses the reversible oxidation of myo-inositol to scyl lo-inosose (2-keto-inositol). The activity with scyllo-inosose and NAD H was a 75-times higher than with myo-inositol and NAD. At pH 8.0 the equilibrium of the reaction strongly favours the production of myoinos itol. The K-m values for myo-inositol and scyllo-inosose were 430 mM a nd 1.3 mM, respectively. The dehydrogenase is specific for myo-inosito l and scyllo-inosose. The enzyme was purified about 205-fold to appare nt homogeneity with a specific activity of 63 mu kat mg protein(-1) wi th scyllo-inosose as substrate. The M-r of the subunits was 42 000 and of the native enzyme ca 189 000. (C) 1997 Elsevier Science Ltd. All r ights reserved.