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

SYNOPSIS. Three‐day‐old cultures of Y and MR strains of Trypanosoma 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. In addition, 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, however, inhibited the uptake of arginine by 10‐day culture cells of the Y strain by a mixed‐type of inhibition. Arginine also inhibited the 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.