Pyruvate transport across the plasma membrane of the bloodstream form of Trypanosoma brucei is mediated by a facilitated diffusion carrier

The characteristics of pyruvate transport across the plasma membrane in the bloodstream form of Trypanosoma brucei were studied using [¹⁴C]pyruvate in combination with the silicone-oil centrifugation technique. We present evidence for the existence of a facilitated diffusion carrier in the plasma membrane of T. brucei which specifically mediates the translocation of pyruvate. The uptake of pyruvate followed saturation kinetics (K_m 1.96 ± 0.28 mM; C_max 36.61 ± 1.15 nmol pyruvate/30 sec.mg protein), after correction of the data for a nonsaturable diffusion component. The uptake of pyruvate was competitively inhibited by a number of (oxo)monocarboxylic acids, including pyruvate analogs and metabolically related substances, but not by L-lactate. The transport exhibited the phenomenon of transacceleration, indicative for the involvement of a facilitated diffusion carrier. The carrier is highly specific for pyruvate and differs from other known monocarboxylate carriers present in the mitochondrial and/or plasma membrane of other eukaryotic cells in that it does not transport L-lactate.