Pepsin catalyzed hydrolysis

Pepsin catalyzed hydrolysis gave the four peptides shown m blue m Figure 27 10 (Their sequences were determined m separate experiments) These four peptides contain 27 of the 30 ammo acids m the B chain but there are no points of over lap between them... 

Fahmey (148). The pepsin-catalyzed hydrolysis of the racemic phenyl cycloalkyl sulfites 99 was found to be hi ly enantioselective, and it gave the unreacted sulfites 99 in optically active form. 

Transpeptidation experiments. The pepsin-catalyzed hydrolysis of Leu-Tyr-Leu gives the product Leu-Leu, which can be formed from the acyl transfer shown in equation 16.31.166,167... 

It is clear that this mechanistic interpretation is not unique, because there is no direct evidence for the proposed intermediates. For example, alternative possible explanations are (1) The amino group in the aminoenzyme may not be covalently bound, but may merely be activated by the enzyme and (2) similarly, the acyl transfer reaction of equation 16.31 could occur by the direct attack of Leu-Tyr-Leu on the enzyme-bound Leu-Tyr-Leu. However, M. S. Silver and S, L. T. James169,170 have proposed a further interpretation, based on the observation that small peptides stimulate the pepsin-catalyzed hydrolysis of other peptides by being first synthesized into larger peptides in a condensation reaction that is the reverse of the hydrolytic step e.g., equations 16.33. The idea of the condensation of two small peptides to give a larger peptide at a rate that is relatively fast compared with hydrolysis of the small peptides is quite reasonable... 

Figure 6. Arrhenius plot for Greenland cod pepsin-catalyzed hydrolysis of hemoglobin at pH 1.9 (53).

Pepsin-catalyzed hydrolysis gave the fonr peptides shown in bine in Fignre 27.10. (Their seqnences were determined in separate experiments.) These fonr peptides contain 27 of the 30 amino acids in the B chain, but there are no points of overlap between them. 

Hayashi and Kameda have reported 40% to 70% decreases in pepsin-catalyzed hydrolysis of lysozyme, soybean protein, casein and rlbonuclease A due to alkali-treatment under slightly milder conditions than ours (16, 29). Friedman, Zahnley and Masters reported an 80% decrease in digestibility of sodium hydroxide-treated casein measured as hydrolysis by trypsin (17). However, trypsin is specific for lysyl residues and lysine levels decreased to about half control values during the alkali-treatment, with a concomitant Increase in LAL formation. The somewhat lower digestibilities reported by these laboratories compared to our observations may be due to LAL formation in the proteins other than zein. 

Reference to Figure 2 indicates some of the other important residues in the neighborhood of the two active aspartic acid side chains. It is clear that Asp-32 and Asp-215 are in very close contact (preliminary measurements from the Kendrew model indicate that the two carboxyl groups are approximately coplanar and about 2.6 A separates two of the oxygen atoms). The pH profiles of k or pepsin-catalyzed hydrolysis of small synthetic... 

The presence of anhydride intermediates during the course of the hydrolysis of sulfite esters catalyzed by pepsin was proposed by May and Kaiser (14). Studies of the catalysis of sulfite ester hydrolysis by model carboxylate species indicated that the presence of anhydride intermediates could be detected in such reactions by the use of nucleophilic trapping reagents (17). Based on the results of the model studies, we were encouraged to attempt to trap the hypothetical anhydride intermediates formed in the pepsin-catalyzed hydrolysis of a sulfite ester using hydroxylamine as the trapping agent, which could lead to the identification of the active sites involved in this reaction. 

The mechanism shown in Figure 2 has been proposed for the pepsin-catalyzed hydrolysis of sulfite esters (14). This mechanism involves the postulated formation of an anhydride intermediate (V). If such a species is formed in the pepsin-catalyzed hydrolysis of sulfite esters. 

Figure 2. Proposed mechanism for the pepsin-catalyzed hydrolysis of sulfite esters.

Since the nature of the groups involved in anhydride formation in the pepsin-catalyzed hydrolysis of PTFS was elucidated, we attempted to identify the particular residues taking part in catalysis. 

Kinetic Constants of Pepsin Catalyzed Hydrolysis of Synthetic Substrates... 

Roncal, T., Oviedo, A., Armentia, I. L. D., et al. (2007). High yield production of monomer-free chitosan oligosaccharides by pepsin catalyzed hydrolysis of a high deacetylation degree chitosan. Carbohydr Res., 342, 2750-2756. 

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