Catalyzes the reversible NADPH-dependent reduction of scyllo-inosose (SIS) to scyllo-inositol (SI). Cannot use NADH instead of NADPH. May be involved in reduction of not only SIS but also various oxidized compounds manifested upon stressful conditions. NADP(+) + scyllo-inositol = H(+) + NADPH + scyllo-inosose Is constitutively expressed, even in the absence of both myo-inositol and scillo-inositol (PubMed:20133360). Is up-regulated under certain stressful conditions (PubMed:22383849). Cells lacking this gene show normal growth on SI as well as on glucose or myo-inositol (MI) as the sole carbon source. Belongs to the Gfo/Idh/MocA family.