[Allosterism of acidic alcohol dehydrogenase (class III ADH) of mouse liver and its role in alcohol metabolism].

Two major ADH isozymes of mouse liver, basic ADH (Class I) and acidic ADH (Class III) were purified and the effects of various hydrophobic substances (t-butanol, butyramide, trifluoroethanol, trichloroacetic acid, stearic acid, oleamide, phenylalanine and norleucine) on their activities were investigated. All these hydrophobic substances activated acidic ADH with a range of from 15 to 560%, and reversely inactivated basic ADH activity with a range of from 10 to 100%, when 150 mmol/l ethanol was used as a substrate. Among these substances, t-butanol, which was the most potent activator of acidic ADH, enhanced the activity by 560% and completely inactivated basic ADH at a concentration of 1.0 mol/l. Kinetics studies demonstrated that the activation of acidic ADH by the hydrophobic substances was due to marked decreases of Km for ethanol in spite of decreases of Vmax, suggesting these substances were positive allosteric effectors for the isozyme. The inactivation of basic ADH by the hydrophobic substances was due to a decrease of Vmax without changing Km for ethanol. These results indicate that the activities of two ADH isozymes are regulated reversely by the hydrophobicity of the reaction environment which changes their kinetics constants. The ELISA method using the isozyme-specific antibody demonstrated that the content of acidic ADH in mouse liver was about 7 times larger than that of basic ADH (5.3 +/- 0.86 vs 0.72 +/- 0.06 mg/g-liver). In the light of the hydrophobic regulation of ADH isozyme activities and their liver contents, the role of acidic ADH on alcohol metabolism may be more predominant than basic ADH in the liver under hydrophobic condition.