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Pepsin ester hydrolysis

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. [Pg.160]

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. [Pg.168]

Figure 2. Proposed mechanism for the pepsin-catalyzed hydrolysis of sulfite esters. Figure 2. Proposed mechanism for the pepsin-catalyzed hydrolysis of sulfite esters.
Pish protein concentrate and soy protein concentrate have been used to prepare a low phenylalanine, high tyrosine peptide for use with phenylketonuria patients (150). The process includes pepsin hydrolysis at pH 1.5 ptonase hydrolysis at pH 6.5 to Hberate aromatic amino acids gel filtration on Sephadex G-15 to remove aromatic amino acids incubation with papain and ethyl esters of L-tyrosine and L-tryptophan, ie, plastein synthesis and ultrafiltration (qv). The plastein has a bland taste and odor and does not contain free amino acids. Yields of 69.3 and 60.9% from PPG and soy protein concentrate, respectively, have been attained. [Pg.471]

Enzymes of the pepsin family rarely catalyze the hydrolysis of esters, with the exceptions of, for example, esters of L-/3-penicillactic acid and some sulfinic acid esters. Under suitable conditions, i. e., low pH, high enzyme concentration, and formation of an insoluble peptide, aspartic peptidases are able to catalyze the synthesis of peptides [71] [72],... [Pg.80]

Similarly, lysine has been incorporated into gluten hydrolyzate and lysine, threonine and tryptophan have been individually incorporated into zein hydrolyzates. Lysine, methionine, and tryptophan were incorporated simultaneously into hydrolyzates of protein from photosynthetic origin. A very interesting application of this procedure involved the preparation of low-phenylalanine plasteins from a combination of fish protein concentrate and soy protein isolate by a partial hydrolysis with pepsin then pronase to liberate mainly phenylalamine, tyrosine, and tryptophan, which were then removed on sephadex G-15. Desired amounts of tyrosine and tryptophan were added back in the form of ethyl esters and a plastein suitable for feeding to infants afflicted with phenylketonuria was produced. [Pg.282]

Carboxybiotin. The structure of biotin suggested that bicarbonate might be incorporated reversibly into its position 2. However, this proved not to be true and it remained for F. Lynen and associates to obtain a clue from a "model reaction." They showed that purified P-methylcrotonyl-CoA carboxylase promoted the carboxylation of free biotin with bicarbonate (H14C03 ) and ATP. While the carboxylated biotin was labile, treatment with diazomethane (Eq. 14-6) gave a stable dimethyl ester of N-l -carboxybiotin.53 54 The covalently bound biotin at active sites of enzymes was also successfully labeled with 14C02 Treatment of the labeled enzymes with diazomethane followed by hydrolysis with trypsin and pepsin gave authentic N-l -carboxybiocytin. It was now clear that the cleavage of ATP is required to couple the C02 from HCOs to the biotin to form carboxybiotin. The enzyme must... [Pg.725]

In Table II are shown the results from kinetic studies with commercially available gastric and pancreatic enzymes. Trypsin was strongly inhibited, at least at a low concentration of casein as substrate. The hydrolysis of benzoyl arginine ethyl ester (BAEE) by trypsin was non-competitively inhibited, giving a 30% reduction of Vmax at 0.5 mg/ml of the LMW fraction. Carboxypepti-dase A, and to a lesser extent carboxypeptidase B, were non-competitively inhibited as well. Pepsin and chymotrypsin were not affected by the conditions used in these assays. [Pg.408]

The nutritional quality of a protein can be increased by the plastein reaction (46). Following partial hydrolysis of a protein by pepsin, the ethyl ester of a limiting amino acid such as methionine or cystine, or a partial hydrolysate of another protein which is limiting in another amino acid residue, can be added to the hydrolysate and covalently linked through plastein formation. [Pg.105]

The mechanism of amide- and ester-hydrolyzing enzymes is very similar to that observed in the chemical hydrolysis by a base. A nucleophilic group from the active site of the enzyme attacks the carbonyl group of the substrate ester or amide. This nucleophilic chemical operator can be either the hydroxy group of a serine (e.g., pig fiver esterase, subtifisin, and the majority of microbial lipases), a carboxyl group of an aspartic acid (e.g., pepsin) [3], or the thiol functionality of cysteine (e.g., papain) [4-6]. [Pg.31]

The kinetics of the formation of chlorosulphonic acid from sulphuric acid have been followed in a hetero neous system the activation ener is 23.8 kcal mol. The hydrolysis of sulphite esters in carboxylate buffer has been examined as a model for the corresponding pepsin-catalysed process. The carboxylate anion acts as a nucleophile, attacking the sulphur, with the formation of a mixed anhydride. The rate of the alkaline hydrolysis of para-substituted ethyl benzenesulphinates has been studied. This reaction, which occurs with S—O bond fission, occurs by nucleophilic attack on sulphur to form a tetrahedral intermediate. The value of A5 v — 30 cal mol and p = + 1.60. It is concluded that ki>k-u and the reaction is... [Pg.112]

In addition to the types of synthetic substrate for pepsin mentioned above, others include depsipeptides such as Z-His-Phe(4N02)-Pla-OMe, whose rapid hydrolysis showed that pepsin can act as an esterase provided the primary specificity requirements are met (30), sulfite esters such as bis-p-nitrophenyl sulfite (31,32) which are also cleaved rapidly, and various more resistant compounds such as Tfa-Phe (33) and Leu-Tyr-Leu or Leu-Tyr-NH2 (34), whose mode of cleavage by pepsin has also suggested various hypotheses about the mechanism of pepsin action. [Pg.134]

Fahmey and Reid (11) discovered that pepsin catalyzes the hydrolysis of sulfite esters. Extensive kinetic studies on these reactions have been performed in our laboratory (12-15). The following observations suggest that the active sites involved in the hydrolysis of sulfite esters and in the hydrolysis of peptides may be identical, or may at least overlap ... [Pg.159]


See other pages where Pepsin ester hydrolysis is mentioned: [Pg.146]    [Pg.146]    [Pg.61]    [Pg.171]    [Pg.174]    [Pg.175]    [Pg.2]    [Pg.227]    [Pg.12]    [Pg.582]    [Pg.16]    [Pg.494]    [Pg.156]    [Pg.80]    [Pg.725]    [Pg.130]    [Pg.198]    [Pg.135]    [Pg.174]    [Pg.89]   
See also in sourсe #XX -- [ Pg.61 ]




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