Purification and characterization of aldehyde dehydrogenase from rat liver mitochondrial matrix

Aldehyde dehydrogenase (EC 1.2.1.3) has been purified to homogeneity from Sprague-Dawley rat liver mitochondrial matrix; its specific activity with propionaldehyde (1 mM at pH 9.0) is 1.4 mumol/min/mg. It has a native molecular weight of ca. 260,000 daltons, a subunit weight of 54,000 daltons and separates into two bands on isoelectric focusing (pI, 5.15 and 5.30); its extinction coefficient at 280 nm for 1 mg/ml solution is 1.2 and 280/260 nm ratio is 1.6. The enzyme prefers NAD over NADP as the coenzyme; the Km for NADP (67,000 microM) is three orders of magnitude greater than that for NAD (61 microM); the Km for acetaldehyde is 2 microM and for propionaldehyde is 0.8 microM at pH 7.0. The enzyme is reversibly inhibited by chloral (Ki = 3 microM) but is resistant to disulfiram inhibition. In addition another aldehyde dehydrogenase, first observed in the mitochondrial matrix during isoelectric focusing, has been partially purified. It has a Km for propionaldehyde of 0.7 mM and an isoelectric point of 6.4. Its activity with glutamic-gamma-semialdehyde (Km = 0.13 mM) is ca. 20 times higher than with propionaldehyde identifying the enzyme as glutamic-gamma-semialdehyde dehydrogenase (EC 1.5.1.12).