2-methyl-3-oxopropanoate + CoA + H2O + NAD(+) = H(+) + hydrogencarbonate + NADH + propanoyl-CoA A number of isoforms are produced. According to EST sequences. Belongs to the aldehyde dehydrogenase family. In contrast to other members of the family, the conserved Glu residue in position 94 is replaced by an Arg. Its activity is therefore unsure.