Metabolism of [3-13C]-pyruvate by cysticerci of Taenia crassiceps

Carbon-13 decoupled 1H spin-echo nuclear magnetic resonance (NMR) spectra, with and without 13C population inversion, of extracts of Taenia crassiceps cysticerci incubated in media containing [3-13C]-pyruvate showed 13C enrichment in alanine, lactate, acetate, succinate, and citrate. Labeling in the latter three metabolites provides substantial evidence that the malic enzyme reaction in this cestode also functions in the direction opposite to that in which it is normally portrayed. The direct passage of pyruvate from the cytosol to the mitochondrion is suggested by the greater percentage of 13C detected in acetate relative to succinate.