Molecular Pharmacology, Vol 9, 199-208, Copyright © 1973 by the American Society for Pharmacology and Experimental Therapeutics

The Specific Binding of Vitamin A Acid to Equine Liver Alcohol Dehydrogenase

¹ Department of Chemistry, University of California, San Diego, La Jolla, California 92037

Addition of vitamin A acid to solutions of liver alcohol dehydrogenase (EC 1.1.1.1) results in a significant quenching of the protein fluorescence. The quenching attains a maximum value when equimolar amounts of the reactants are present. The quenching is pH-dependent, and indicates the involvement of a group on the protein with a pK value of 7.6. Vitamin A acid is a competitive inhibitor of the oxidation of ethanol, but does not significantly affect the reverse reaction. On the other hand, vitamin A amide competitively inhibits the reduction of acetaldehyde, without significantly affecting the oxidation of ethanol. The vitamin A acid protects the essential thiol groups against carboxymethylation to a lesser degree than reduced coenzymes but to a higher degree than ethanol.

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ACKNOWLEDGMENTS It is a pleasure to thank Professor N. O. Kaplan for his support and encouragement during this work. The author is also indebted to Dr. P. H. van Leeuwen, N. V. Philips-Duphar, Weesp, The Netherlands, for his generous gift of the crystalline vitamin A acid isomers and the all-trans vitamin A aldehyde.