3-hydroxy-2-methylpropanoate + NAD(+) = 2-methyl-3-oxopropanoate + H(+) + NADH Amino-acid degradation; L-valine degradation. Homodimer. Higher level in kidney, liver, and heart than in muscle. Belongs to the HIBADH-related family. 3-hydroxyisobutyrate dehydrogenase subfamily.