Canine Liver Aldehyde Dehydrogenases: Distribution, Isolation, and Partial Characterization

Canine liver aldehyde dehydrogenases (ALDH) (aldehyde:NAO oxi‐doreductase; EC 1.2.1.3) tm analogous to enzymes identified in human and other mammalian liver tissue in regard to subcellular localization, affinity for substrates, inhibition by disutfiram, 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, HA, and IIB have been isolated from canine Kver 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 HA and IIB appear to be mitochondrial in origin. ALDH IA has ‐a high K_m for acetaldehyde (3 mM) and propionaldehyde (4 mM). ALDH IB and IIA have K_m values for acetaldehyde and propionalde hyde in the range of 4–60 μM. ALDH IIB has the lowest K_m of the four isoenzymes for acetaldehyde and propionaldehyde (1–3 μM). All four isoenzymes have K_m values for NAD in the range of 4–70 MM. ALDH IB and IIA an 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 isoen zymes as determined by gel filtration chromatography.