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Rabbit liver class III alcohol dehydrogenase: a cathodic isoform with formaldehyde dehydrogenase activity
W M Keung1, L Kunze, B Holmquist
1Center for Biochemical and Biophysical Sciences and Medicine, Harvard Medical School, Boston, MA 02115, USA.
Alcoholism, Clinical and Experimental Research
|August 1, 1995
Summary
Researchers purified a rabbit liver enzyme, class II alcohol dehydrogenase (ADH), revealing it functions as a glutathione-dependent formaldehyde dehydrogenase, similar to human and rat class III ADH. This enzyme plays a key role in alcohol metabolism.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Multiple forms of alcohol dehydrogenase (ADH) exist in rabbit liver, categorized as class I, II, and III based on electrophoretic mobility.
- Previous studies identified distinct classes of ADH, but the specific functions and characteristics of each class require further elucidation.
Purpose of the Study:
- To purify and characterize the class II alcohol dehydrogenase (ADH) from rabbit liver homogenate.
- To compare the biochemical and kinetic properties of rabbit class II ADH with other known ADH enzymes, particularly human class III ADH.
Main Methods:
- Purification of rabbit liver homogenate using starch gel electrophoresis.
- Isolation of the class II ADH enzyme to homogeneity via ion exchange and affinity chromatography.
- Characterization of enzyme properties including isoelectric point, molecular weight, amino acid composition, and kinetic parameters.
Main Results:
- The purified rabbit class II ADH is a homodimer with a molecular weight of approximately 80,000 and an isoelectric point of 7.7.
- It exhibits similar amino acid composition and kinetic parameters to human class III ADH for primary alcohol oxidation.
- The enzyme functions as a glutathione-dependent formaldehyde dehydrogenase, catalyzing the oxidation of S-hydroxymethylglutathione and hemithiolacetal of 8-thiooctanoic acid.
Conclusions:
- Rabbit class II ADH is biochemically and functionally analogous to human and rat class III ADHs, acting as a formaldehyde dehydrogenase.
- The enzyme displays distinct substrate kinetics, with Michaelis-Menten behavior for longer-chain primary alcohols and non-saturating kinetics for ethanol at high concentrations.