Involved in cholesterol degradation. Catalyzes the conversion of propanal to propanoyl-CoA, using NAD(+) and coenzyme A. Has a broad substrate specificity, and can also use acetaldehyde, butyrlaldehyde, isobutyrlaldehyde and pentaldehyde as substrates. CoA + NAD(+) + propanal = H(+) + NADH + propanoyl-CoA acetaldehyde + CoA + NAD(+) = acetyl-CoA + H(+) + NADH Unlike HsaF, HsaG is active both in the presence and absence of its partner enzyme. kcat is 9.4 sec(-1) with acetaldehyde as substrate (in the presence of HsaF). kcat is 19.0 sec(-1) with acetaldehyde as substrate (in the absence of HsaF). kcat is 11.1 sec(-1) with propanal as substrate (in the presence of HsaF). kcat is 23.8 sec(-1) with propanal as substrate (in the absence of HsaF). kcat is 7.3 sec(-1) with butyrlaldehyde as substrate. kcat is 5.8 sec(-1) with isobutyrlaldehyde as substrate. kcat is 7.8 sec(-1) with pentaldehyde as substrate. kcat is 9.6 sec(-1) with coenzyme A as substrate (in the presence of HsaF). kcat is 15 sec(-1) with coenzyme A as substrate (in the absence of HsaF). kcat is 7.6 sec(-1) with NAD(+) as substrate (in the presence of HsaF). kcat is 3.9 sec(-1) with NAD(+) as substrate (in the absence of HsaF). kcat is 3.4 sec(-1) with NADP(+) as substrate. Monomer. Forms an heterotetramer composed of two aldolase (HsaF) and two dehydrogenase (HsaG) subunits. Belongs to the acetaldehyde dehydrogenase family.