Ralph G. Somes

Heterogeneity of amino acid transport activity in the avian erythrocyte

Abstract 1. 1. Variability in amino acid transport activity has been studied in the chicken erythrocyte. 2. 2. Proline transport was observed to undergo a transient posthatch intensification. 3. 3. Leucine transport was found to become stabilized by 6–7 weeks of age in approximately two-thirds of the birds surveyed; in other birds, typically those with high values, transport activity declined over a subsequent test period of 4 weeks. 4. 4. Significant differences in leucine transport were found to exist between adult chickens sampled at 2-week intervals. 5. 5. Leucine transport rates were found to cluster about several discrete values when many individual chickens were surveyed. 6. 6. The basis for such differences in transport activity is discussed.

Amino acid transport and intracellular Na+ and K+ content of chicken erythrocytes genetically selected for high and low leucine transport activity

1. Amino acid transport and intracellular Na+ and K+ content have been studied in two lines of chickens, one high and the other low uptake, selected for their ability to transport leucine into erythrocytes. 2. Low line birds were less effective in absorbing glycine into erythrocytes than were high line birds, the difference in transport being due to a difference in maximal flux (Vmax), but not in apparent affinity for transport sites (Kt). 3. In contrast to glycine uptake, the greater ability of the high line to absorb lysine was found to be due to a difference in both Vmax and Kt. 4. High line erythrocytes were also observed to contain slightly more K+ (about 5%) and about 20% less Na+ than low line erythrocytes. 5. These results are discussed in terms of the ion dependency of amino acid transport.

Sodium-ion dependence of glycine and lysine transport in chicken erythrocytes genetically selected for high and low leucine transport activity

Amino acid transport was studied in two lines of chickens, one high and the other low uptake, selected for their ability to transport leucine into erythrocytes. On the basis of the number of mol of substrate transferred, medium Na+ was found to be more effective in stimulating glycine and lysine transport into high line cells than into low line cells. Glycine transport in both lines was stimulated by medium Na+ to a greater degree than was lysine transport. In the absence of medium Na+, glycine transport was not significantly different in the two lines. In the absence of medium Na+, lysine transport in the high line was about five-fold greater than in the low line. The transport differences between the lines are probably due to differences in several distinct genetic determinants.