Absorption of two proline containing peptides by rat small intestine in vivo.

Abstract

SUMMARY1. Glycyl-L-proline and L-prolyl-glycine are two dipeptides that are poorly hydrolysed by brush border peptide hydrolases in vitro. The present study was undertaken to investigate in vivo intestinal absorption of the two dipeptides in male Wistar rats. A steady-state perfusion technique has been used and jejunal and ileal absorption studied by comparing rates of absorption of constituent amino acids from dipeptide and equivalent equimolar amino acid solutions.2. Glycine and proline were absorbed at the same or faster rates during perfusion of 10 mM glycyl-L-proline than during perfusion of its equivalent equimolar amino acid solution. Conversely, the two constituent amino acids were absorbed at slower rates during perfusion of 10 mM-L-prolylglycine than during perfusion of its equivalent amino acid solution. As expected very low concentrations of free amino acids were detected during the jejunal dipeptide perfusions but higher concentrations were detected during the ileal perfusions.3. The addition of 40 mM L-prolyl-glycine to the 10 mM glycyl-L-proline solution did not affect the rates of disappearance of glycyl-L-proline. The addition of 40 mM glycyl-L-proline to 10 mM L-prolyl-glycine however had a significant inhibitory effect on the disappearance of L-prolyl-glycine. It is concluded that the two dipeptides may be absorbed by different peptide transport systems.

Absorption of Hydroxyproline-Containing Peptides in Vascularly Perfused Rat Small Intestinein Situ

“…2,23) It has previously been demonstrated that Pro-Gly and Gly-Pro were poorly hydrolyzed by brush border membranes in intestine epithelial cells 24) and that both dipeptides may be absorbed by different peptide transport systems. 15,24) Moreover, dipeptidyl aminopeptidase IV is known as a proline-specific peptidase associated with the intestinal brush border membrane, 25) and prolyl peptides are efficiently and sequentially hydrolyzed from the carboxyl terminus by the combined action of angiotensin-converting enzyme and carboxypeptidase P. 16) These enzymes may play an important role in the digestion and assimilation of prolinecontaining peptides by the intestines.…”

“…In the previous studies, 2 to 40 mM concentrations of dipeptides had been used as substrates for the intestinal perfusion experiments. [15][16][17] To obtain the base-line level for the absorption, the perfusate was initially collected at two times before injecting the peptide into the gut lumen. Thus, ten minutes after beginning, 1 ml of the test peptide solution (20 mM as for Hyp) was injected into the jejunum lumen at t ¼ 0 min.…”

Immunohistochemical localization of dipeptidyl peptidase IV in rat digestive organs.

“…It has been suggested that di-and tripeptides can be transported into the intestinal cells by specific carrier systems which are different from those involved in the transport of free amino acids (10). It is noteworthy that glycyl-proline is a dipeptide very poorly hydrolyzed by brush border enzymes (16) and has affinity for the dipeptide carrier system of the small intestine (7,17). DPP IV cleaves NH2-ternimal dipeptides, X-Pro, from polypeptides, and Gly-Pro-Y is known to be one of the most suitable substrates for this enzyme (11, 15).…”

Sites of dipeptide hydrolysis in relation to sites of histidine and glucose active transport in hamster intestine.

“…1967;Fern et al 1969;Peters, Modha & MacMahon, 1969;Adibi, 197 1;Fogel & Adibi, 1974) and pro-gly (Lane, Silk & Clark, 1975). It should be borne in mind that there may not be the same localization of peptidases within the intestinal epithelial cells of different animals and that different methods of examining the activity of peptidases even in a given animal may yield dissimilar results (Wells et at.…”