Studies on transport of amino acids from peptides by rat small intestine in vitro. Synthesis, properties and uptake of a photosensitive tetrapeptide.
By comparison with what is known of disaccharides transport, it has been suggested that intestinal aminopeptidase N could, hydrolyze, on the surface of the microvillus membrane, oligopeptides longer than tripeptides and itself subserve the translocation function for the amino acids released from these peptides. This article describes the synthesis of the tritiated azido-tetrapeptides p-azido[3H]phenylalanyl-alanyl-glycyl-glycine containing L or D-alanine. The synthesized products possess a function which displays all the characteristics of an aryl-azide. The photosensitive tetrapeptide formed with LAla-Gly-Gly is as good a substrate for porcine and rat aminopeptidases N as unmodified peptides while the tetrapeptide formed with DLa-Gly-Gly is not hydrolyzed at all. In addition a pattern of stepwise hydrolysis could be demonstrated and aminopeptidase N is the only exopeptidase present in the mucosal cells capable of utilizing the modified tetrapeptide as substrate. Uptake assays performed on everted rings of jejunum with the azido-tetrapeptide as substrate have shown that: (a) the azido-tetrapeptide is not transported intact but must be hydrolyzed first; (b) p-azido-phenylalanine is not released in the external medium and therefore its observed uptake is not from the bulk medium and (c) the azido-D-tetrapeptide is only accumulated by passive diffusion. These observations suggest the presence on the brush border membrane of an aminopeptidase-related transport system.
D000596:Amino Acids / Q000378:metabolism*; D000626:Aminopeptidases / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D018826:CD13 Antigens; D002855:Chromatography, Thin Layer; D006868:Hydrolysis; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D007421:Intestine, Small / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D009842:Oligopeptides / Q000378:metabolism*; D010777:Photochemistry; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity
D000596:Amino Acids; D009842:Oligopeptides; C033833:4-azidophenylalanyl-alanyl-glycyl-glycine; D000626:Aminopeptidases; D018826:CD13 Antigens