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. Belongs to the aldehyde dehydrogenase family. Truncated N-terminus.