Separation and functions of two acyl CoA transferases from Ascaris lumbricoides mitochondria

Many invertebrates accumulate propionate, or products derived from propionate, as products of fermentation. Evidence has been reported that the nematode, Ascaris suum, the cestode, Spirometra mansonoides, and the trematode, Fasciola hepatica, accumulate propionate by means of an adenosine triphosphate (ATP)-generating decarboxylation of succinate. To generate energy, an acyl coenzyme A (CoA) transferase that would transfer CoA to succinate is required as one component of the sequence of reactions. Recently, an acyl CoA transferase was isolated from Ascaris mitochondria and purified to electrophoretic homogeneity. However, upon examination of the substrate specificities of this enzyme, it was found essentially to lack the ability to use succinate or succinyl CoA as an acceptor or donor of CoA, respectively. Therefore, this transferase could not serve to activate succinate. This article describes the isolation of an additional acyl CoA transferase from Ascaris mitochondria that appears to be unique in its substrate specificity and that could easily account not only for the activation of succinate but also for the regulation of succinate metabolism primarily in the direction of decarboxylation to propionate. This is in contrast with mammalian tissues, which act in the opposite direction by catalyzing the fixation of CO2 into propionate, thereby forming succinate and accounting for the glycogenic nature of dietary propionate. Possible functions of the two acyl CoA transferases are discussed.