RETINAL OXIDATION ACTIVITY AND BIOLOGICAL ROLE OF HUMAN CYTOSOLIC ALDEHYDE DEHYDROGENASE

The major cytosolic aldehyde dehydrogenase isozyme (ALDH1) exhibits strong activity for oxidation of retinal to retinoic acid, while the major mitochondrial ALDH2 and the stomach cytosolic ALDH3 have no such activity. The K(m) of ALDH1 for retinal is about 0.06 mumol/l at pH 7.5, and the catalytic efficiency (V(max)/K(m)) for retinal is about 600 times higher than that for acetaldehyde. Thus, ALDH1 can efficiently produce retinoic acid from retinal in tissues with low retinal concentrations (< 0.1 mumol/l). The gene for ALDH1 has hormone response elements. These findings suggest that the major physiological substrate of human ALDH1 is retinal, and that its primary biological role is generation of retinoic acid resulting in modulation of cell differentiation including hormone-mediated development.