Involved in the anaerobic succinate degradation pathway (PubMed:8328804, PubMed:8444151, PubMed:8550525). Catalyzes the interconversion of gamma-hydroxybutyrate (GHB) and succinic semialdehyde (SSA) (PubMed:8328804, PubMed:7606170, PubMed:8550525). 4-hydroxybutanoate + NAD(+) = H(+) + NADH + succinate semialdehyde Binds 1 Fe(2+) ion per subunit. Binds 2 Cu(2+) ions per subunit. Inactivated by oxygen. Optimum pH is 6.1 for the reduction of succinic semialdehyde and pH 9.4 for the oxidation of 4-hydroxybutanoate. Homodimer. Induced by growth on ethanol plus succinate. Belongs to the iron-containing alcohol dehydrogenase family.