Rat liver constitutive and phenobarbital-inducible cytosolic aldehyde dehydrogenases are highly homologous proteins that function as distinct isozymes.
Rat liver contains two class 1 aldehyde dehydrogenases (ALDHs): a constitutive isozyme (ALDH1) and a phenobarbital-inducible isozyme (ALDH-PB). Defining characteristics of mammalian class 1 ALDHs include a homotetrameric structure, high expression in liver, sensitivity to the inhibitor disulfiram, and high activity for the oxidation of retinal. It is often presumed that ALDH-PB is the rat ortholog of mammalian ALDH1, and the identity of rat ALDH-PB is commonly interchanged with ALDH1. In this study, we characterized recombinant rat liver cytosolic ALDH1 and ALDH-PB. Previous reports indicate that ALDH-PB is a homodimer; however, we found by mass spectrometry and gel electrophoresis that it is a homotetramer. ALDH1 mRNA was highly expressed in untreated rat liver, while ALDH-PB had very weak expression, in contrast to a previous report that ALDH-PB mRNA is expressed in untreated rat liver. Rat liver ALDH1 had a high affinity for retinal (K(m) = 0.6 microM), while no oxidation by ALDH-PB could be detected with 20 microM retinal. ALDH1 was more efficient at oxidizing acetaldehyde, propionaldehyde, and benzaldehyde and was more sensitive to disulfiram inhibition. We conclude that rat liver ALDH1 is the ortholog of mammalian liver ALDH1. Furthermore, despite a high level of sequence identity and classification as a class 1 ALDH, ALDH-PB does not function like ALDH1. ALDH-PB is not merely an inducible ALDH1 isozyme; it is a distinct ALDH isozyme.
Kathmann
E C
EC
Clinical Pharmacology Unit, Department of Molecular Pharmacology and Experimental Therapeutics, and Biomedical Mass Spectrometry Facility, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
Naylor
S
S
Lipsky
J J
JJ
D000444:Aldehyde Dehydrogenase / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D000080924:Aldehyde Dehydrogenase 1 Family; D000595:Amino Acid Sequence; D000818:Animals; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology*; D004221:Disulfiram / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D015636:Magnesium Chloride / Q000494:pharmacology; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010634:Phenobarbital / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D050697:Retinal Dehydrogenase; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity / Q000187:drug effects
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D012333:RNA, Messenger; D011994:Recombinant Proteins; D015636:Magnesium Chloride; D000080924:Aldehyde Dehydrogenase 1 Family; D000444:Aldehyde Dehydrogenase; C523119:Aldh1a1 protein, rat; D050697:Retinal Dehydrogenase; D004221:Disulfiram; D010634:Phenobarbital