RABBIT LIVER CLASS-III ALCOHOL-DEHYDROGENASE - A CATHODIC ISOFORM WITH FORMALDEHYDE DEHYDROGENASE-ACTIVITY

Electrophoresis of rabbit liver homogenate on starch gel followed by a ctivity staining revealed multiple forms of alcohol dehydrogenase (ADH ) which, based on their electrophoretic mobilities, had been tentative ly labeled as class ''I,'' class ''II,'' and class ''III'' ADHs. The c lass II enzyme has now been purified to homogeneity by ion exchange an d affinity chromatography and, except for an isoelectric point of 7.7, closely resembles human class III ADH. It is a homodimer of molecular weight near 80,000 with a similar amino acid composition and comparab le kinetic parameters for the oxidation of primary alcohols. Like the rat, human, and Escherichia coli class III ADHs, the rabbit enzyme is a glutathione-dependent formaldehyde dehydrogenase, and catalyzes the oxidation of S-hydroxymethylglutathione and the hemithiolacetal of 8-t hiooctanoic acid. Ethanol up to 3 M does not saturate the enzyme, wher eas longer chain primary alcohols exhibit Michaelis-Menten kinetics.