Comparative Kinetics of Arginine and Lysine Transport by Epimastigotes and Trypomastigotes from Two Strains of Trypanosoma cruzi*

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Abstract
Three-day old cultures of Y and MR strains of T. cruzi had a higher rate of lysine and arginine uptake than 10-day cultures. Amino acid uptake by cells of the MR strain was consistently higher than that of the Y strain. Flagellates separated on DEAE-cellulose columns have normal structure, motility and infectivity; they have higher rates of lysine and arginine uptake than the original 3- and 10-day cultures. Passage through DEAE-cellulose columns modified the kinetic behavior of amino acid transport systems in the flagellate membranes. Methionine inhibited uncompetitively uptake of lysine and arginine by MR and Y strains. Lysine inhibited arginine uptake by both strains by an uncompetitive mechanism. Lysine inhibited the uptake of arginine by 10-day culture cells of the Y strain by a mixed-type of inhibition. Arginine inhibited lysine uptake of both strains by an uncompetitive mechanism. In all experiments, beyond a certain level, a further increase in inhibitor concentration resulted in a decreased inhibition, which eventually disappeared altogether. Inhibition of amino-acid uptake by any of the substances tested was not observed after passage of flagellates through a DEAE-cellulose column. A model for amino acid transport was formulated which includes a recognition site amenable to modulation by effectors.

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