Sodium dependence and counterflow of some amino acids in chick intestine

By incubating chicken intestinal rings in buffer containing either sodium or mannitol, it was demonstrated that uptake of L-lysine and L-histidine is sodium dependent. Double reciprocal plots of the data indicated that Vmax was independent of sodium concentration. KM values, however, were increased considerably in the absence of the metal, indicating a decreased affinity of the amino acid for a hypothetical carrier. A failure to demonstrate mobile carriers for L-lysine and L-arginine in chick intestine is reported. Counterflow results are briefly discussed in terms of fixed binding sites.