Catalyzes the NAD-dependent oxidation of 2-aminomuconic semialdehyde of the kynurenine metabolic pathway in L-tryptophan degradation. 2-aminomuconate 6-semialdehyde + H2O + NAD(+) = (2Z,4E)-2-aminomuconate + 2 H(+) + NADH Amino-acid degradation; L-kynurenine degradation. Belongs to the aldehyde dehydrogenase family.