Pepsin Activity

The pepsin, activated by cleavage of a proenzyme, has two putative active site domains comprising hydrophobic-hydrophobic-Asp-Thr-Gly amino acids, is potentially glycosylated and has a free cysteine residue which may allow it to form dimers, as in the case of human and Plasmodium falciparum-derived aspartyl proteases (Longbottom et al., 1997). However,... 

In Fig. 3, the pepsin dissolved in HC1, without interaction with any solid, showed a maximum at 272 nm. After interaction with the disordered cancrinite and the intermediate phase, a small decrease in the absorbance maximum of the pepsin spectrum was observed. This small decrease is due to the pepsin adsorption on the solid surfaces. The pepsin activity was also determined by the proteolysis reaction of a denatured haemoglobin solution at different times. Fig. 4 shows the obtained results. One can see, that the enzymatic activities (determined as absorbance), presented by the tested solids were very similar among them. These results show that pepsin enzymatic activity is not lost after the contact the pepsin with the tested solids. Therefore, the absorbance decrease observed in Fig. 4, is produced by the pepsin adsorption on the tectosilicate surface, and not by chemical reactions between pepsin and the tectosilicates... 

Selected entries from Methods in Enzymology [vol, page(s)] Pepsin Activation energy, 63, 243-245 isotope exchange, 64, 10 kinetic constants, 63, 244 kinin-releasing enzyme, 80, 174 porcine, homology to cathepsin D, 80, 578 spectrokinetic probe,... 

Hj-receptor antagonists almost completely block secretion of hydrochloric acid in the stomach in response to most stimuli. These drugs play a major role in treating stomach ulcers associated with hypersecretion, because they have the ability to reduce both the volume of stomach secretion and overall acidity as well as pepsin activity. 

Cimetidine is a representative of first-generation antihistamine drugs that block H2 receptors. The main pharmacological effect of cimetidine is the suppression of gastric juice secretion associated with H2 receptors of the stomach walls. It suppresses both basal and stimulated hyckochloric acid produced by food as well as histamine and gastrine, which simultaneously lower pepsin activity. 

Ranitidine is a second-generation H2-receptor-blocking drug. Like cimetidine, ranitidine suppresses both basal and stimulated hydrochloric acid produced by food, histamine, gastrin, and acetylcholine. It simultaneously reduces pepsin activity and is used for treating stomach and duodenum ulcers as well as other conditions accompanied by elevated acidity of the gastrointestinal tract. Synonyms of this drag are zantac, azantac, raniplex, ranidil, and others. 

Figure 2. Stereo view of pepstatin bound in the R. chinensis pepsin active site. C-3 of statine carrying an OH group is indicated by the . Availability for hydrogen bonding is indicated by closeness of carboxyl groups of Asp-220 and Asp-32 to the statine hydroxyl and to each other.

Mixed protein/polysaccharide micro-beads have also been found to be promising delivery vehicles for immobilized bifidobacteria (Guerin et al, 2003). Such micro-beads were made by a transacylation reaction involving the formation of amide bonds between protein and alginate (Levy and Edwards-Levy, 1996). This produces a membrane on the bead surface, protecting the immobilized bifidobacteria against both the very acidic conditions (pH 1-2) and the pepsin activity in the stomach. 

Decrease acidity within lumen of the esophagus, causing an increase in intraesophageal pH and a decrease in pepsin activity... 

Emmons (1970) experienced significant inactivation when commercial pepsin and pepsin-calf rennet mixtures were diluted with high-pH, hard water 10 min before adding them to the cheese vat. Mickelsen and Ernstrom (1972) reported that mixtures of porcine pepsin and calf rennet were stable between pH 5.0 and 6.0, but that pepsin activity was lost from the mixture aboire pH 6.0. This loss was shown to be entirely due to pepsin instability. Below pH 6.0 chymosin activity was destroyed by pepsin. 

Linklater (1961) reported that bovine pepsin accounted for only 0 to 6% of the milk-clotting activity of commercial rennet extracts. He used porcine pepsin as a reference standard. Bovine pepsin has increased in use as a coagulant because of the practice of extracting the stomach from older calves and adult cattle. More recently, Sellers (1982) reported that 85 to 95% of the proteolytic activity of calf rennet is due to chymosin and the remainder is from bovine pepsin. Adult bovine rennets preparations may contain 55 to 60% bovine pepsin. Mixtures of calf rennet and porcine pepsin may contain 40 to 45% chymosin, 5 to 10% bovine pepsin, and 50% porcine pepsin. Mixtures of adult bovine rennet and porcine pepsin typically contain 20 to 25% chymosin, 40 to 45% bovine pepsin, and 30 to 40% porcine pepsin activity (McMahon and Brown 1985). 

Pohl, J., and Dunn, B. M. (1988). Secondary enzyme-substrate interactions kinetic evidence for ionic interactions between substrate side chains and the pepsin active site. Biochemistry, 27, 4827-4834. 

During last decades the domains C-2 symmetry (the dyad rotation symmetry) of low-B palindrome was established in many enzymes (chymotrypsin, trypsin, aspartyl proteinases, HIV-1 protease, carboxypeptidase A, phospholipase A-2 ribonuclease, etc.) (Lumry, 2002 and references therein). It is proposed that the pair domain closure causes constrain of pretransition state complex that activates cleavage or formation of chemical bonds. Thus control of strong bonds by the cooperation of many matrix or knots bonds takes place. As an example, in the active site of carboxypeptidase A the zinc ion is attached to one of the catalytic domains by histidine 69 and glutamine 72 and connected by hystidine 196 to the second domain. Similar structures were found in the chymotrypsin and pepsin active sites where protons are driven under compression of the domains closure. 

Lipase (Microbial) Activity for Medium- and Long-Chain Fatty Acids, (S3)105 Lysozyme Activity, (S3)106 Maltogenic Amylase Activity, 804 Milk-Clotting Activity, 805 Pancreatin Activity, 805 Pepsin Activity, 807 Phospholipase A2 Activity, 808 Phytase Activity, 808 Plant Proteolytic Activity, 810 Proteolytic Activity, Bacterial (PC), 811 Proteolytic Activity, Fungal (HUT), 812 Proteolytic Activity, Fungal (SAP), 813 Pullulanase Activity, 814 Trypsin Activity, 814 Enzyme Assays, 786 Enzyme-Hydrolyzed (Source) Protein,... 

The basic controversy now revolves around the problem of the existence of a separate pepsin active at pH 1.5-2.0 and a separate gastric cathepsin (gastricsin) active at pH 3.2-3.5. The alternative concept is that the activity at pH 1.5-2.0 and at 3.2-3.5 belongs to a similar protease (pepsin), with the difference that one is derived from the ftmdic glands (fundic pepsin) and the other from the pyloric glands and perhaps chief neck cells (pyloric pepsin) (T22, T24). 

In fiuther work of these authors, chromatography on Amberlite IRC-50 XE-64 columns yielded two sharply delineated fractions differing in proteolytic activity curves (R4, R5, T3-T5a). Pepsin activity was eluted at effluent pH of 4.0, gastricsin at effluent pH of 4.4. Proteases eluted... 

Antacids Antacids neutralize hydrochloric acid and reducing pepsin activity. Two types of antacids are ... 

Antacids neutralize hydrochloric acid and reduce pepsin activity. 

The antiulcerogenic effect of the bark of V. africana was also reported using different experimental models. Tan and collaborators (2, 49) showed the cytoprotection of aqneons extracts for the gastric mucosa against erosive action of corrosive agents (HCl/ EtOH). Thns, V. africana possess anti-ulcer properties and these properties were not related with an increase on mucus production, or reduced pepsin activity, however the cytoprotection was related to a mechanism involving the physico-chemical re-enforcement of the gastric mucous layer. 

Protein digestion begins in the stomach, where protein is denatured by the low pH and is exposed to the action of pepsin. The low pH also provides the optimal H+ concentration for pepsin activity. The zymogen precursor pepsinogen (M.W. 40,000) is secreted by the chief cells and is converted to pepsin (M.W. 32,7(K)) in the acid medium by removal of a peptide consisting of 44 amino acid residues. This endopeptidase hydrolyzes peptide bonds that involve the carboxyl group of aromatic amino acid residues, leucine, methionine, and acidic residues (Table 12-5). The products consist of a mixture of oligopeptides. 

Majumdar, A. P., Bilateral adrenalectomy Effect of tryptophan on protein synthesis and pepsin activity in the stomach of rats, Scand.. Gastroenterol., 14, 949, 1979. 

Potential pepsin activity of untreated pepsinogen taken as 100. 

Figure 9. Dependence of specific optical rotation (----) and potential pepsin activity...

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