Reductase with a preference for aliphatic substrates. Can also act on small aromatic aldehydes, steroid aldehydes and some ketone substrates. an alditol + NAD(+) = an aldose + H(+) + NADH an alditol + NADP(+) = an aldose + H(+) + NADPH Monomer. Detected at very low levels in urinary bladder, testis and jejunum. By FGF-1 (By similarity). Up-regulated by calpain inhibitor I (N-acetyl-leucyl-leucyl-norleucinal/ALLN). Belongs to the aldo/keto reductase family.