Pepsin hydrolysis

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. 

Pepsin Hydrolysis of proteins Porcine stomach Digestive aid... 

Figure 5. Arrhenius plot for arctic cod pepsin hydrolysis of hemoglobin...

Pepsin Hydrolysis of polypeptides, including those with bonds adjacent to aromatic or dicarboxylic L-amino acid residues, yielding peptides of lower molecular weight. 

The improvement of the whipping properties of enzymatically modified soy proteins and casein has already been of use in the baking industry. For example, Gunther (25) has patented a method for producing these products by pepsin hydrolysis. 

BaderschneiderB, CrevelRWR, EarlLK, LalljieA, Sanders DJ, Sanders D (2002). Sequence analysis and resistance to pepsin hydrolysis as part of an assessment of the potential allergenicity of ice structuring protein type III HPLC 12. Food Chem. Toxicol, 40 965-978. 

Fig. 10 Typical RP-HPLC profiles of whey protein hydrolysates T = 37°C, 60 min hydrolysis time) (A) pepsin hydrolysis, pH2, three major fractions were designated PI P3 (B) trypsin hydrolysis, pH 8, nine major fractions were designated T1-T9 (C) Alcalase hydrolysis, pH8, 12 major fractions were designated A1-A12.

Schwartz, H. R., Nerurkar, L. S., Spies, J. R., Scanlon, R. T., and Bellanti, J. A., 1980, Milk hypersensitivity RAST studies using new antigens generated by pepsin hydrolysis of beta-lactoglobulin, Ann. Allergy 45 242. 

Pepstatin is a strong competitive inhibitor of pepsin which is produced by various strains of actinomycetes (14). The structure (Fig.6) contains an unusual amino acid 4-amino-3-hydroxy-6-methyl-heptanoic acid (statine). Tang has proposed that the statine residue of pepstatin resembles the transition state for pepsin hydrolysis of peptide bonds (15, see also Chapter 12 in this volume). If this is so and the central statine residue binds at the catalytic site with its side chain in the Si subsite, then we note (Fig.6) that the interactions at all the other subsites are favorable or neutral. The P subsites are listed with the assumption that central residue bridges two subsites (Si and SJ). 

The pepsin-catalyzed transpeptidation reactions, both the amino transfer (14) and the acyl transfer types (15) (Fig.6), suggest the formation of at least two intermediates in which fragments of the substrate are bound to the enzyme. For a long time, however, no transpeptidation reaction of the amino transfer type could be found for substrates containing a blocked COOH-terminal carboxyl group adjacent to the bond being cleaved. The existence of the amino-enzyme in the pepsin hydrolysis pathway of conventional substrates was therefore somewhat doubtful (16). As for the transpeptidation of the acyl transfer type, it has been found so far only on substrates with a free NH2-terminal amino group. 

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... 

There are two main classes of proteolytic digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolyzed. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. They are the first enzymes to act, yielding a larger number of smaller fragments, eg, pepsin in the gastric juice and trypsin, chymotrypsin, and elastase secreted into the small intestine by the pancreas. Exopeptidases catalyze the hydrolysis of peptide bonds, one at a time, fi"om the ends of polypeptides. Carboxypeptidases, secreted in the pancreatic juice, release amino acids from rhe free carboxyl terminal, and aminopeptidases, secreted by the intestinal mucosal cells, release amino acids from the amino terminal. Dipeptides, which are not substrates for exopeptidases, are hydrolyzed in the brush border of intestinal mucosal cells by dipeptidases. 

The proteases are secreted as inactive zymogens the active site of the enzyme is masked by a small region of its peptide chain, which is removed by hydrolysis of a specific peptide bond. Pepsinogen is activated to pepsin by gastric acid and by activated pepsin (autocatalysis). In the small intestine, trypsinogen, the precursor of trypsin, is activated by enteropeptidase, which is secreted by the duodenal epithelial cells trypsin can then activate chymotrypsinogen to chymotrypsin, proelas-tase to elastase, procarboxypeptidase to carboxypepti-dase, and proaminopeptidase to aminopeptidase. 

Since FPIAs are conducted as homogeneous immunoassays, they are susceptible to effects from endogenous fluorophores and from intersample variations. Such problems and others due to the sample matrix are largely avoided by sample dilutions of several hundredfold. Low-affinity, nonspecific binding of tracers to sample proteins, when present in sufficiently high concentrations, can result in a falsely elevated polarization signal. Interference from sample proteins can be eliminated when warranted, by proteolytic hydrolysis with pepsin.(46)... 

Fig. 3.10. Mechanism of peptide bond hydrolysis by pepsin, an aspartic endopeptidase [2]...

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],... 

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. 

The stomach secretes pepsinogens, which are inactive proteolytic enzymes, and protons - the high concentration of which initiates hydrolysis of the pepsinogens to form active pepsins, which then continue their own activation, via an autocatalytic, hydrolysis (Appendix 4.1). 

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