Table 1.

Human ALDH genes and gene products

Gene	Protein Description
ALDH1A1	ALDH1A1 is a cytosolic enzyme that oxidizes retinal, acetaldehydes and 3-deoxyglucosone (a product of protein deglycation and a potent glycating agent).
ALDH1A2	ALDH1A2 is a cytosolic enzyme that is integrally involved in the oxidation of retinal to retinoic acid during embryonic development. Aldh1a2(-/-) mice are embryolethal.
ALDH1A3	ALDH1A3 is a cytosolic retinaldehyde-metabolizing enzyme.
ALDH1B1	ALDH1B1 is a mitochondrial enzyme that metabolizes acetaldehyde.
ALDH1L1	ALDH1L1 is a fusion protein comprising three domains: a formyl transferase domain at the amino terminal, a centrally-located formyltransferase carboxyl terminal domain and an aldehyde dehydrogenase domain at its carboxyl terminal (Figure 2).
ALDH1L2	ALDH1L2 shares ≈73% identity with ALDH1L1; no functional data have been reported for this protein.
ALDH2	ALDH2 is a mitochondrial enzyme involved in the oxidation of acetaldehyde and the metabolites of dopamine and norepinephrine, DOPAL and DOPEGAL, respectively.
ALDH3A1	ALDH3A1 is a multifunctional enzyme that plays a significant role in the cellular response to oxidative stress.
ALDH3A2	ALDH3A2 is a microsomal enzyme that oxidizes medium to long-chain fatty aldehydes.
ALDH3B1	ALDH3B1 is a cytosolic protein that oxidizes medium- and long-chain saturated and unsaturated aliphatic aldehydes.
ALDH3B2	ALDH3B2 is a putative ALDH with no functional data available.
ALDH4A1	ALDH4A1 catalyzes the irreversible conversion of Δ1-pyrroline-5-carboxylate (derived from either proline or ornithine) to glutamate, necessary to connect the urea cycle with the tricarboxylic acid cycle.
ALDH5A1	ALDH5A1 is the succinate semialdehyde dehydrogenase involved in the last step of GABA catabolism, converting GABA to succinate semialdehyde.
ALDH6A1	ALDH6A1 is the methylmalonate semialdehyde dehydrogenase that catalyzes the irreversible oxidative decarboxylation of malonate and methylmalonate semialdehydes to acetyl- and propionyl-CoA, respectively.
ALDH7A1	ALDH7A1 metabolizes α-aminoadipic semialdehyde, generated during lysine catabolism.
ALDH8A1	ALDH8A1 appears to be involved in 9-cis-retinoic acid biosynthesis.
ALDH9A1	ALDH9A1 catalyzes the oxidation of γ-aminobutyraldehyde and betaine aldehyde, a γ-trimethylaminobutyraldehyde.
ALDH16A1	No functional information exists in the literature for this enzyme.
ALDH18A1	ALDH18A1 is a bi-functional ATP- and NAD(P)H-dependent mitochondrial inner-membrane protein having both γ-glutamyl kinase and γ-glutamyl phosphate reductase activities