Mechanism of action of adenosylcobalamin. 3-Fluoro-1,2-propanediol as substrate for propanediol dehydrase. Mechanistic implications

Abstract

3-Fluoro-1,2-propanediol has been found to be a substrate for propanediol dehydrase and has very similar binding and catalytic constants compared to the natural substrate. The only isolable products of the reaction are acrolein and inorganic fluoride; with 3-fluoro-3,3-dideuterio-l,2-propanediol as substrate, only 3,3-dideuterioacrolein is obtained. These results indicate that the primary product of the reaction is 3-fluoropropionaldehyde which spontaneously loses hydrogen fluoride to yield acrolein. The similar kinetic parameters for the fluorinated as compared to the normal substrate suggest that significant charge does not develop on the fluorinated or, by implication, the natural substrate during any rate-limiting steps of the reaction. These results support a radical, as contrasted to an ionic pathway for reactions involving adenosylcobalamin and diol dehydrase.