Structural and functional divergence of class II alcohol dehydrogenase--cloning and characterisation of rabbit liver isoforms of the enzyme.
cDNAs coding for class II alcohol dehydrogenase were isolated from a rabbit-liver cDNA library. Deduced amino acid sequences show that isozymic forms of rabbit class II alcohol dehydrogenase exist, with a positional identity of 88.4%. A high variability in structure of class II alcohol dehydrogenase between the species is also reflected in function. The rabbit II-1 isozyme shows common characteristics with the human enzyme, but has a lower Km value for ethanol, 4.2 mM. The II-2 isozyme shows restriction for aliphatic alcohols longer than pentanol. For shorter alcohols the II-2 form has similar Km values as the II-1 isozyme, 5.5 mM for ethanol, but is a low activity variant with a 10-fold decrease in k(cat) values compared with II-1. Nevertheless, II-2 has a higher specificity for benzoquinone than II-1 due to a lower Km value, 80 microM compared with 1 mM, and is in this sense more like the human class II enzyme. In addition a rabbit class III alcohol dehydrogenase cDNA was isolated that encodes a typical class III enzyme/glutathione-dependent formaldehyde dehydrogenase. The finding of isozymic forms of class II alcohol dehydrogenase is in line with the evolution of the system of medium-chain alcohol dehydrogenases with different enzymes, different classes and different isozymes and further underline the complexity of the entire mammalian alcohol dehydrogenase system.
Svensson
S
S
Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
Hedberg
J J
JJ
Höög
J O
JO
D000426:Alcohol Dehydrogenase / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D000445:Aldehyde Oxidoreductases / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D006801:Humans; D015151:Immunoblotting; D007527:Isoenzymes; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D011817:Rabbits; D017386:Sequence Homology, Amino Acid
D007527:Isoenzymes; D000426:Alcohol Dehydrogenase; C020145:formaldehyde dehydrogenase (glutathione); D000445:Aldehyde Oxidoreductases