The absorption of free and "peptide" amino acids in the small intestine of chicks.

1. The accumulation of free L-tryptophan and glycine in the small intestine of chicks, as well as of amino acids released at the hydrolysis of glycyl-L-tryptophan, glycyl-L-leucine and glycyl-L-valine, was studied under experiments in vitro with accumulating preparations of chicks intestinal mucosa. 2. At the incubation of accumulating mucosal preparations (AMP) in a medium containing the investigated compounds in the presence of sodium ions (140 mM) or an equal amount of potassium ions, the existence of 2 ways of their transport was found: sodium-independent and sodium-dependent. The latter is decisive for the transport of free L-tryptophan. 3. In the case of peptide L-tryptophan the power of both mechanisms is about the same, but in case of free glycine the sodium-independent mechanism is dominant. 4. The transport of peptide glycine is realized only through the sodium-independent mechanism. 5. The existence of amino acid transport against the gradient is noted by replacing sodium by potassium ions in the incubation medium. Its absence was observed at the incubation of AMP under anaerobic conditions. 6. The study of kinetics of L-tryptophan accumulation showed that the replacement of sodium ions by potassium ones in the incubation medium is accompanied by a decrease of Kt from 2.23 to 0.84 mM as well as of V from 4.54 to 0.84 mM/min per cm. 7. Modifiers (L-valine, L-threonine, L-alpha-alanine) in concentrations of 100 mM inhibit drastically the accumulation of free and peptide L-tryptophan in the mucosa of chick small intestine, and this effect is mainly related to the action of sodium-dependent transport mechanisms.