The in vitro oxidation of ethanol and retinol by human liver and cattle retina was studied. Purification of human liver alcohol dehydrogenase yielded similar increases in the specific activity and recovery of ethanol and retinol oxidizing activities, and antibodies to the purified enzyme produced similar inhibition of the oxidation of both substrates. The specific activity of oxidation of ethanol as substrate was 150 times higher than of retinol by liver alcohol dehydrogenase, while the Michaelis-Menten constant was 50-fold smaller for retinol oxidation. In cattle retina, the specific activities and Michaelis-Menten constants for both ethanol and retinol oxidation were of comparable magnitude. Ethanol was found to be an inhibitor of retinol oxidation by both human liver and cattle retina. The inhibition was competitive with respect to retinol at ethanol concentrations of 1.8 × 10-4 M and below, and mixed or noncompetitive at higher ethanol concentrations. The inhibition constant, Ki, was 3.6 × 10-4 M for human liver alcohol dehydrogenase. The maximum inhibition of retinol oxidation by cattle retina that could be obtained by increasing ethanol concentrations was 38%. It is suggested that both ethanol and retinol are oxidized by the same enzyme in the liver, but not in the retina.
ASJC Scopus subject areas
- Pathology and Forensic Medicine
- Molecular Biology
- Clinical Biochemistry