| Abstract: | 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. |
