Canine liver aldehyde dehydrogenases: distribution, isolation, and partial characterization

Canine liver aldehyde dehydrogenases (ALDH) (aldehyde:NAD oxidoreductase; EC 1.2.1.3) are analogous to enzymes identified in human and other mammalian liver tissue in regard to subcellular localization, affinity for substrates, inhibition by disulfiram, and effects of magnesium ions on enzyme activity. Aldehyde dehydrogenase activity is distributed in the mitochondrial, microsomal, and cytosolic fractions of the cell. Four isoenzymes designated ALDH IA, IB, IIA, and IIB have been isolated from canine liver via ammonium sulfate fractionation, ion-exchange chromatography, and affinity chromatography. Based on cell fractionation followed by enzyme isolation, ALDH IA and IB appear to be extramitochondrial whereas ALDH IIA and IIB appear to be mitochondrial in origin. ALDH IA has a high Km for acetaldehyde (3 mM) and propionaldehyde (4 mM). ALDH IB and IIA have Km values for acetaldehyde and propionaldehyde in the range of 4-60 microM. ALDH IIB has the lowest Km of the four isoenzymes for acetaldehyde and propionaldehyde (1-3 microM). All four isoenzymes have Km values for NAD in the range of 4-70 microM. ALDH IB and IIA are sensitive to inhibition by disulfiram whereas ALDH IA and IIB are resistant. Magnesium ions inhibit ALDH IA, IB, and IIA whereas ALDH IIB activity is stimulated approximately 2-fold. Magnesium ions do not affect molecular weight estimates of the isoenzymes as determined by gel filtration chromatography.