The Synthesis of Butyric and Caproic Acids from Ethanol and Acetic Acid by Clostridium Kluyveri

Abstract

When C. kluyveri is grown anaerobically in a medium containing ordinary ethanol and synthetic acetic acid labeled in the carboxyl group with C14, labeled butyric and caproic acids are formed. The butyric acid so formed has C14 almost equally distributed between the carboxyl and [beta] positions. The [alpha] and [gamma] positions are inactive. The caproic acid has 1/3 of its C14 in the carboxyl group; probably the [beta] and [DELTA] positions are also labeled, though this has not been proved. No active CO2 is formed from carboxyl-labeled acetic acid. This indicates that CO2 is not an intermediate in these reactions. The C14 content of the residual acetic acid is much lower than that of the initial acetic acid. This evidently results from the oxidation of ethanol to acetic acid or a related compound in isotopic equilibrium with it. When C. kluyveri is grown with ordinary ethanol and synthetic carboxyl-labeled butyric acid, C14 is found in caproic acid but not in acetic acid. The active caproic acid so formed contains almost no activity in its carboxyl group. The above facts are consistent with the view that the formation of butyric acid involves a condensation between acetic acid or a reactive derivative thereof, such as acetylphosphate, formed by the anaerobic oxidation of ethanol, and a 2d molecule of acetic acid. The condensation product is then reduced to butyric acid. Caproic acid formation involves a condensation of the carboxyl group of butyric acid or some related C4 compound, like butyrylphosphate, with the methyl group of acetic acid.