Inducible aldehyde dehydrogenases from rat liver cytosol

Two rat hepatic cytoplasmic isozymes of aldehyde dehydrogenase, φ, induced by phenobarbital treatment, and τ, 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 φ and τ isozymes, respectively. Estimates of molecular weights from gel filtration chromatography gave values of 118,000 Da for φ and 106,000 Da for τ. An isoelectric point for the τ enzyme of 6.5 was determined in an electrofocusing column, and approximately 7.2 for φ by immunoelectrophoresis. Both enzymes can oxidize a wide variety of aldehyde substrates, with K m 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 τ enzyme is able to use NADP as cofactor. The measured K m for φ at pH 7.2 for acetaldehyde was 1.97 m m and for τ, 12.1 m m. Both enzymes showed similar inhibition characteristics with sodium arsenite and disulfiram, although the φ enzyme tended to be slightly more sensitive to all inhibitors.