Two main ALDH enzymes metabolize the acetaldehyde produced during ethanol oxidation (see Table 3) (Crabb et al. 2004; Hurley et al. 2002): ALDH1, which is found in the fluid filling the cells (i.e., the cytosol) and is encoded by the ALDH1A1 gene, and ALDH2, which is found in the mitochondria and is encoded by the ALDH2 gene. The ALDH1A1 gene extends over about 52 kb on chromosome 9, and ALDH2 extends over 43 kb on chromosome 12. Both genes have a similar structure with 13 exons. Moreover, the proteins they encode are 70 percent identical in sequence and very similar in structure (Hurley et al. 2002).
