Effect of Glycylglycine on Absorption from Human Jejunum of an Amino Acid Mixture Simulating Casein and a Partial Enzymic Hydrolysate of Casein Containing Small Peptides

Abstract

A jejunal perfusion technique was used in normal volunteer subjects to study jejunal absorption of amino acid residues from a partial enzymic hydrolysate of casein in which about 50% of the amino acids existed as small peptides and from an equivalent mixture of free amino acids. The effect of a high concentration of dipeptide glycylglycine on absorption of amino acid residues from these preparations was studied to quantify the importance of mucosal uptake of intact peptides during absorption of the partial hydrolysate of casein. Glycylglycine significantly inhibited absorption of several amino acid residues (aspartic acid + asparagine, serine, glutamic acid + glutamine, proline, alanine, phenylalanine, threonine and isoleucine) from the free amino acid mixture, whereas it significantly inhibited absorption of only 2 (serine, glutamic acid + glutamine) from the peptide-containing partial casein hydrolysate. The effect of glycylglycine on absorption of amino acids om the mixture of free amino acids was apparently due to inhibition of amino acid uptake by free glycine liberated from the dipeptide during perfusion. The reason for failure of glycylglycine to cause extensive inhibition of absorption from the partial hydrolysate may be that glycylglycine is only a weak inhibitor of peptide uptake. The possibility that some peptides are taken up by a system unavailable to glycylglycine should also be considered.