An Examination of the Metabolism of Thiamin by Rat Liver Alcohol Dehydrogenase

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Abstract
Thiamin and its thiazole moiety, 5-(2-hydroxyethyl)-4-methylthiazole, have been examined as substrates for purified rat liver alcohol dehydrogenase (RLADH) (EC 1.1.1.1). Although thiamin itself is a poor substrate for the enzyme, its thiazole moiety is oxidized at a faster rate than ethanol. With incubation times greater than 5 minutes, the major product of the in vitro reaction of the thiazole moiety of thiamin with RLADH is the corresponding acid, 4-methylthiazole-5-acetic acid (thiazole acetic acid). A possible mechanism for this RLADH catalyzed two-step oxidation of the thiazole moiety of thiamin first to 4-methylthiazole-5-acetaldehyde followed by oxidation of this compound to thiazole acetic acid is discussed. The RLADH inhibitor pyrazole was administered in vivo followed by radiolabeled thiamin and its thiazole moiety. Urine was collected for 24 hours, and the levels of radiolabeled thiamin acetic acid and thiazole acetic acid were determined. The results of these experiments provide evidence that RLADH is involved in the in vivo metabolism of thiamin and its thiazole moiety to their corresponding acids.