An NAD+ dependent enzyme that catalyzes the oxidation 3-methyl-2-oxobutanoate to 2-methylpropanoyl-CoA. It plays a role in the degradation of VALINE; LEUCINE; and ISOLEUCINE.

The addition of an organic acid radical into a molecule.

An enzyme that plays a role in the VALINE; LEUCINE; and ISOLEUCINE catabolic pathways by catalyzing the oxidation of 2-methyl-3-oxopropanate to propanoyl-CoA using NAD+ as a coenzyme. Methylmalonate semialdehyde dehydrogenase deficiency is characterized by elevated BETA-ALANINE and 3-hydropropionic acid.