Multifunctional enzyme mediating important protective effects. Metabolizes betaine aldehyde to betaine, an important cellular osmolyte and methyl donor. Protects cells from oxidative stress by metabolizing a number of lipid peroxidation-derived aldehydes. Involved in lysine catabolism. H2O + NAD(+) + nonanal = 2 H(+) + NADH + nonanoate (S)-2-amino-6-oxohexanoate + H2O + NAD(+) = 2 H(+) + L-2-aminoadipate + NADH betaine aldehyde + H2O + NAD(+) = glycine betaine + 2 H(+) + NADH an aldehyde + H2O + NAD(+) = a carboxylate + 2 H(+) + NADH H2O + hexanal + NAD(+) = 2 H(+) + hexanoate + NADH H2O + NAD(+) + octanal = 2 H(+) + NADH + octanoate (E)-non-2-enal + H2O + NAD(+) = (E)-non-2-enoate + 2 H(+) + NADH (E)-4-hydroxynon-2-enal + H2O + NAD(+) = (E)-4-hydroxynon-2-enoate + 2 H(+) + NADH Amine and polyamine biosynthesis; betaine biosynthesis via choline pathway; betaine from betaine aldehyde: step 1/1. Homotetramer. Abundant in hepatoma cells and fetal cochlea, ovary, eye, heart, adrenal gland, liver and kidney. Low levels present in adult peripheral blood leukocytes and fetal brain, thymus, spleen, skeletal muscle, lung and tongue. The disease is caused by variants affecting the gene represented in this entry. Belongs to the aldehyde dehydrogenase family. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus. Aberrant splicing. Extended N-terminus.