Uptake of leucine and lysine in chicken red blood cells of varying density.

1. Reproducible separations of chicken red blood cells into three density ranges have been achieved employing Ficoll density layer centrifugation techniques. 2. Carrier-mediated lysine uptake was observed to be much greater than that of leucine and was found to decrease with an increase in cell density due to a change in the maximal uptake rate (Vmax) but not in apparent uptake affinity (Kt). 3. Little difference was seen between cells of varying density in their ability to absorb leucine. 4. Since red blood cell density increases with cell age, these results suggest that the uptakes of leucine and lysine are affected differentially during cell aging.