Muscle tricarboxylic acid cycle in Ascaris lumbricoides var. suis

Abstract

Muscle homogenates of Ascaris lumbricoides var. suis metabolized succinate-2,3-C 14, acetate-1-C 14 and citrate-1,5-C 14 resulting in the formation of C 14O 2. When muscle strips were used, C 14O 2 formation from succinate-2,3-C 14 and from acetate-1-C 14 was inhibited considerably by monofluoroacetate. The incubation of succinate-2,3-C 14 or acetate-2-C 14 with particle fractions from Ascaris muscle produced C 14-citrate. Also the activities of isocitrate dehydrogenase (NADP specific), fumarase, α-Ketoglutarate dehydrogenase, malate dehydrogenase, aconitase, condensing enzyme and aceto-CoA kinase were detected in various preparations from Ascaris muscle by appropriate assay methods. These findings suggested the occurrence of a tricarboxylic acid cycle in Ascaris muscle. On the other hand, examination of C 14-labeled succinate and fumarate catabolism has revealed that the carboxylic acid metabolism in Ascaris muscle could proceed through a dismutation reaction between carboxylic acids of different oxidation levels. The functioning of the tricarboxylic acid cycle in Ascaris muscle appeared to be considerably limited on account of the relatively low activity of terminal oxidase system as well as aconitase, condensing enzyme and pyruvate dehydrogenase. Therefore the physiological role of the cycle might be of a minor importance as compared to the dismutation type reaction.