title: Identification of mouse liver aldehyde dehydrogenases that catalyze the oxidation of retinaldehyde to retinoic acid.
abstract: NAD(P)-linked aldehyde dehydrogenases catalyze the oxidation of a wide variety of aldehydes. Thirteen of these enzymes have been identified in mouse tissues; eleven are found in the liver. Some are substrate-nonspecific; others are relatively substrate-specific. The present investigation sought to determine which of these enzymes are operative in catalyzing the oxidation of retinaldehyde to retinoic acid, a metabolite of vitamin A that promotes the differentiation of epithelial and other cells. Spectrophotometric and HPLC assays were used for this purpose. Enzyme-catalyzed oxidation of retinaldehyde (25 microM) was restricted to the cytosol (105,000 g supernatant fraction) and occurred at a rate of 211 nmol/min/g liver; oxidation of acetaldehyde (4 mM) by this fraction proceeds about ten times faster. At least 90% of this activity was NAD dependent. Of the approximately 10% that was apparently NAD independent, two-thirds was inhibited by 1 mM pyridoxal, a known inhibitor of aldehyde oxidase. Of the six cytosolic aldehyde dehydrogenases, only two, viz. AHD-2 and AHD-7, catalyzed the oxidation of retinaldehyde to retinoic acid. An additional NAD-dependent enzyme, viz. xanthine oxidase (dehydrogenase form), also catalyzed the reaction. Catalysis by AHD-2 accounted for more than 90% of the total NAD-dependent activity. Km values were 0.7, 0.6 and 0.9 microM, respectively, for the AHD-2-, AHD-7- and xanthine oxidase (dehydrogenase form)-catalyzed reaction. AHD-4, an aldehyde dehydrogenase found in the cytosol of mouse stomach epithelium and cornea, did not catalyze the reaction.
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis 55455.
authors.forename: M O
authors.initials: MO
authors.lastname: Lee
authors.forename: C L
authors.initials: CL
authors.lastname: Manthey
authors.forename: N E
authors.initials: NE
authors.lastname: Sladek
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000302:isolation & purification* / Q000378:metabolism; D000818:Animals; D002845:Chromatography / Q000379:methods; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000201:enzymology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D051379:Mice; D008811:Mice, Inbred DBA; D009243:NAD / Q000494:pharmacology; D010084:Oxidation-Reduction; D012172:Retinaldehyde / Q000378:metabolism*; D012995:Solubility; D013053:Spectrophotometry; D014212:Tretinoin / Q000378:metabolism*
chemical_list: D009243:NAD; D014212:Tretinoin; D000444:Aldehyde Dehydrogenase; D012172:Retinaldehyde