Inducible aldehyde dehydrogenases from rat liver cytosol

Two rat hepatic cytoplasmic isozymes of aldehyde dehydrogenase, phi, induced by phenobarbital treatment, and tau, induced by TCDD treatment, have been purified from rat hepatic cytosol by ammonium sulfate fractionation, followed by ion-exchange and affinity chromatography. The specific activities of the two isozymes at pH 9.6 with propionaldehyde as substrate and NAD as cofactor were 2850 and 5250 nmol of NADH/min/mg protein for phi and tau isozymes, respectively. Estimates of molecular weights from gel filtration chromatography gave values of 118,000 Da for phi and 106,000 Da for tau. An isoelectric point for the tau enzyme of 6.5 was determined in an electrofocusing column, and approximately 7.2 for phi by immunoelectrophoresis. Both enzymes can oxidize a wide variety of aldehyde substrates, with Km values ranging from millimolar to micromolar. Long-chain aliphatic and aromatic aldehydes using NAD as cofactor tend to be the best utilized substrates. Only the tau enzyme is able to use NADP as cofactor. The measured Km for phi at pH 7.2 for acetaldehyde was 1.97 mM and for tau, 12.1 mM. Both enzymes showed similar inhibition characteristics with sodium arsenite and disulfiram, although the phi enzyme tended to be slightly more sensitive to all inhibitors.