Absorption of Amino Acids and Oligopeptides

Dipeptides and tripeptides that escape brush border membrane peptidases are actively transported against a concentration gradient by Na -dependent mechanisms. Inside the cell they are hydrolyzed. 

Free amino acids are transported into enterocytes by four active, carrier-mediated, Na+-dependent transport systems remarkably similar to the system for glucose. These systems transport, respectively, neutral amino acids basic amino acids (Lys, Arg, His) and cystine aspartic and glutamic acids and glycine and imino acids. Some amino acids (e.g., glycine) have affinities for more 

Hydrolysis of a synthetic tripeptide by chymotrypsin in the small intestine. The hydrolysis yields PABA, which is absorbed and eventually excreted in the urine. The concentration of PABA is a measure of exocrine pancreatic function. 

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