METABOLISM OF PROPIONIC ACID IN ANIMAL TISSUES

Abstract

The fate of propionic acid in the animal body is of interest since this compound appears to be a product of some metabolic reactions. In ruminants propionic acid is produced through bacterial fermentations in the rumen (1) and can be incorporated into higher odd-numbered fatty acids which have been found to occur in natural fats (2). Propionic acid may normally also arise not only from the @ oxidation of odd-numbered fatty acids but from the degradation of branched aliphatic ammo acids (3-5). Although propionic acid had long been known to undergo oxidation in the animal body, the nature of the intermediary reactions was obscure. Some investigators considered that the primary attack was by CY oxidation, via the sequence propionate += acrylate --, lactate + pyruvate (6-8). However, experiments on the distribution of Cl4 from labeled propionate in tissue glycogen (9) and acetyl groups (lo), or in lactate (11)) showed a complete randomization of the carbon atoms originating from the cr or p position of propionate. When propionate was reisolated, no redistribution of Cl4 was found to have occurred between its cyand P-carbons (10). These results suggested that propionate was irreversibly converted to pyruvate by way of a symmetrical intermediate such as would be formed if propionate or acrylate were first carboxylated to succinate or fumarate, followed by oxidation to oxalacetate and decarboxylation of the latter. This view finally received direct support through the finding of Lardy and Peanasky (12) that extracts of acetone-dried rat liver mitochondria catalyzed an