Pathway of formation of alpha-methylvalerate by Ascaris lumbricoides.

Ascaris lumbricoides is a parasitic intestinal helminth whose metabolism is predominantly anaerobic in the adult stage (1). This organism converts carbohydrate to succinate (2) and a mixture of volatile acids (3, 4). Quantitatively, the major fermentation products are succinate, a-methylbutyrate, and a Cg acid. Saz and Vidrine (5) have demonstrated that succinate is formed by means of COZ fixation into pyruvate and subsequent reduction of the product to succinate. These authors have also shown that Ascaris muscle strips catalyze the formation of propionate and carbon dioxide from succinate. Saz and Weil (6) have presented evidence, based on Cl4 incorporation studies, that a-methylbutyrate was formed as a result of a condensation between the carboxyl carbon of acetate and the a-carbon of propionate or derivatives of these acids. The “acetate” required for the condensation reaction arose from the oxidative decarboxylation of pyruvate. Saz and Gerzon (7) have isolated and identified the Cg acid formed by intact worms, and also by Ascaris muscle strips, as oc-methylvaleric acid. The present study has revealed evidence which indicates that propionate is the precursor of all 6 carbons of oc-methylvalerate formed by this fermentation.