Peptidases intestinal

Amino- peptidase Intestinal epithelium The bond linking the A -terminal amino acid to the rest of the chain 7-4... 

Importantly, both incretins when secreted by the intestine are rapidly degraded by the dipeptidyl peptidase IV (DPPFV), which removed the two amino-terminus histidine-alanine residues, thereby, inactivating the incretins. This enzyme is present at the surface of the epithelial intestinal cells and capillaries in the vicinity of the K and L cells secreting GIP and GLP-1, respectively. It is also present in the... 

A proteolytic cascade occurs when one peptidase activates the next in a proteolytic pathway, and this in turn activates the next and so on. This is a mechanism to amplify the initial signal, because one peptidase molecule can activate many zymogen molecules. Examples of proteolytic cascades include blood coagulation, activation of digestive peptidases in the intestine, and apoptosis. 

The coupling of solute transport in the GI lumen with solute lumenal metabolism (homogeneous reaction) and membrane metabolism (heterogeneous reaction) has been discussed by Sinko et al. [54] and is more generally treated in Cussler s text [55], At the cellular level, solute metabolism can occur at the mucosal membrane, in the enterocyte cytosol, and in the endoplasmic reticulum (or microsomal compartment). For peptide drugs, the extent of hydrolysis by lumenal and membrane-bound peptidases reduces drug availability for intestinal absorption [56], Preferential hydrolysis (metabolic specificity) has been targeted for reconversion... 

The intestinal mucosal peptidases are distributed in the brush border and cytosol of the absorptive cell. There are, however, distinct differences between the brush border and cytosolic peptidases [75], The tetrapeptidase activity is associated exclusively with the brush border enzyme. Furthermore, brush border peptidases exhibit more activity against tripeptides than dipeptides, whereas the cytosolic enzymes show greater activity against dipeptides. Studies have demonstrated that more than 50% of dipeptidase activity was detected in the cytosol [76] and just 10% in the brush border membrane [77]. The brush border enzymes include... 

N Triadou, J Bataille, J Schmitz. Longitudinal study of the human intestinal brush border membrane proteins. Distribution of the main disaccharidases and peptidases. Gastroenterology 85 1326-1332, 1983. 

N Tobey, W Heizer, R Yeh, T Huang, C Hoffner. Human intestinal brush border peptidases. Gastroentrology 88 913-926, 1985. 

S Auricchio, A Stellato, B De Vizia. Development of brush border peptidases in human and rat small intestine. Pediatr Res 15 991-995, 1981. 

Garren K, and Repta A (1988) Buccal drug absorption Comparative levels of esterase and peptidase activities in rat and hamster buccal and intestinal homogenates. Int. J. Pharm. 48 189-194. 

Here, we use intestine-selective and kidney-selective drug delivery to illustrate the targeting of constitutionally expressed peptidases. 

Numerous studies have been published on the in vivo metabolism of peptides. However, these studies are concerned mainly with assessment of pharmacokinetic parameters such as half-life and clearance. Only seldom is the in vivo biotransformation of peptides that contain only common amino acids investigated in any detail, due to the difficulty of monitoring products of proteolysis that are identical to endogenous peptides and amino acids. More importantly, such studies fail to yield mechanistic and biochemical insights. For this reason, we begin here with a discussion of the metabolism of just a few peptides in some selected tissues, namely portals of entry (mouth, gastro-intestinal tract, nose, and skin), plasma, organs of elimination (liver, kidney), and pharmacodynamic sites (brain and cerebrospinal fluid). These examples serve as introduction for the presentation in Sect. 6.4.2 of the involvement of individual peptidases in peptide metabolism. 

Another informative prodrug of TRH is its /V-lauroyl derivative (6.81 R = lauroyl R = R" = H) [200][201], which was absorbed several-fold better by the intestine than TRH, indicating good stability toward intestinal peptidases. It was also far more stable than TRH in plasma. The i.v. administration of this prodrug to rats resulted in bioactivity that was not statistically different than that of TRH, indicating that it is activated in situ to TRH. Thus, lauroyl-TRH appears to be a more promising candidate than the series of carbamates, an outcome that appears impossible to forecast. 

J. P. F. Bai, Influences of Regional Differences in Activities of Brush-Border Membrane Peptidases within the Rat Intestine on Site-Dependent Stability of Peptide Drugs , Life Sci. 1993,53, 1193-1201. 

Peptide and protein drugs must be transported without metabolic degradation to the systemic circulation in order to exhibit or exert their pharmacological action. Although active transport of linear peptides and oligopeptides by intestinal oligopeptide transporters has been reported, overall intestinal absorption of peptides is very poor because of metabolic degradation by peptidases. " ... 

Longer, M.A., Woodley, J.F., and Duncan, R., Comparison of the activities of rat small intestine and colon brush border membrane peptidases, Proc. Int. Symp. Contr. Rel Bioact. Mater., 16 225-226 (1989). 

These proteolytic enzymes are all endopeptidases, which hydrolyse links in the middle of polypeptide chains. The products of the action of these proteolytic enzymes are a series of peptides of various sizes. These are degraded further by the action of several peptidases (exopeptidases) that remove terminal amino acids. Carboxypeptidases hydrolyse amino acids sequentially from the carboxyl end of peptides. They are secreted by the pancreas in proenzyme form and are each activated by the hydrolysis of one peptide bond, catalysed by trypsin. Aminopeptidases, which are secreted by the absorptive cells of the small intestine, hydrolyse amino acids sequentially from the amino end of peptides. In addition, dipeptidases, which are structurally associated with the glycocalyx of the entero-cytes, hydrolyse dipeptides into their component amino acids. 

Small-intestinal secretions. The glands of the small intestine (the Lieberkuhn and Brunner glands) secrete additional digestive enzymes into the bowel. Together with enzymes on the microvilli of the intestinal epithelium (peptidases, glycosidases, etc.), these enzymes ensure almost complete hydrolysis of the food components previously broken down by the endoenzymes. 

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