Ocular alcohol dehydrogenase in the rat: regional distribution and kinetics of the ADH-1 isoenzyme with retinol and retinal

Abstract

Starch-gel electrophoresis of rat ocular tissues shows two anodic isoenzymes of alcohol dehydrogenase (ADH), designated as ADH-1 and ADH-2, ADH-1 is characteristic of the ocular tissues, and corresponds to more than 95% of all ADH activity in the eye. The well known cathodic forms of rat liver ADH, that we named ADH-3, are not observed in the ocular tissues. ADH-1 is detected in retina, pigment epithelium-choroid, ocular fluid, and cornea but not in the lens. The cornea exhibits the highest ADH activity [200 +/- 59 milliunits (munits) mg-1] followed by the pigment epithelium-choroid (11 +/- 7 munits mg-1). Activity in the retina is very small (0.6 +/- 0.2 munit mg-1) and represents only 0.6% of the total activity in the eye. Most of the rat ocular ADH is localized in the cornea (68%) where it could play a significant role in the detoxication of the alcohols of a broad range of structures. Purified ADH-1 shows a low Km for retinol oxidation (20 microM) and for retinal reduction (30 microM) indicating that this isoenzyme may have a function in the metabolism of retinoids. Ethanol competitively inhibits retinol oxidation, but with a very high apparent inhibition constant (0.6 M) demonstrating that the inhibitory effect is not significantly at the usual concentrations found in the blood during ethanol intoxication.