Pepsin

Fc is digested to smaller fragments due to the partial disruption of the three-dimensional structure at the pH used. 

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The activity of an enzyme varies considerably with acidity and there is generally a marked optimum pH for each enzyme. Thus pepsin of the stomach has an optimum pH of 1 4, i.e., it works best in a decidedly acid medium. It is inactive in neutral or alkaline solutions and the latter rapidly destroy it. 

Urease is one of the enzymes which have been obtained in the crystalline state. This has been done by stirring jack bean meal with 30°o aqueous acetone, filtering and allowing the filtrate to remain at o for several hours. The urease which crystallises out is separated by centrifuging and is then recrystallised. Like crystalline pepsin and trypsin, it is a protein. 

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... 

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. 

A pepsin hydrolysate of flounder fish protein isolate has been used as the substrate (40% w/v) for plastein synthesis, using either pepsin at pH 5 or alpha chymotrypsin at pH 7, with an enzyme—substrate ratio of 1 100 w/v at 37°C for 24 h (151). The plastein yields for pepsin and alpha chymotrypsin after precipitation with ethanol were 46 and 40.5%, respectively. 

Pish silage prepared by autolysis of rainbow trout viscera waste was investigated as a substrate for the plastein reaction using pepsin (pH 5.0), papain (pH 6—7), and chymotrypsin (pH 8.0) at 37°C for 24 h (152). Precipitation with ethanol was the preferred recovery method. Concentration of the protein hydrolysate by open-pan evaporation at 60°C gave equivalent yields and color of the final plastein to those of the freeze-dried hydrolysate. 

The resuspended and formulated Fraction II precipitate normally contains some aggregated IgG and trace substances that can cause hypotensive reactions in patients, such as the enzyme prekail ikrein activator (186). These features restrict this type of product to intramuscular adininistration. Further processing is required if products suitable for intravenous adininistration are required. Processes used for this purpose include treatment at pH 4 with the enzyme pepsin [9001-75-6] being added if necessary (131,184), or further purification by ion-exchange chromatography (44). These and other methods have been fiiUy reviewed (45,185,187,188). Intravenous immunoglobulin products are usually suppHed in the freeze-dried state but a product stable in the solution state is also available (189). 

The mechanism by which sucralfate accelerates healing of duodenal ulcers has not been determined. It does not have significant antisecretory, acid neutralizing activity or direct stimulation of ulcer healing. It is known that the mechanism is local rather than systemic. Binding of pepsin or bile salts may contribute to its effect. It is indicated for the short-term therapy of active duodenal ulcers and for maintenance at reduced dosage. 

The enzymatic hydrolysates of milk casein and soy protein sometimes have a strong bitter taste. The bitter taste is frequently developed by pepsin [9001 -75-6] chymotrypsin [9004-07-3] and some neutral proteases and accounted for by the existence of peptides that have a hydrophobic amino acid in the carboxyhc terminal (226). The relation between bitter taste and amino acid constitution has been discussed (227). 

In 1833 an amylase from germinating barley was recovered and called diastase (1). Like malt itself, this product converted gelatinized starch into sugars, primarily maltose. Shordy thereafter, BerzeHus proclaimed the existence of non-living catalysts, and Schwaim (2) reported on his observation and purification of pepsin. 

In 1878 the term enzyme, Greek for "in yeast," was proposed (8). It was reasoned that chemical compounds capable of catalysis, ie, ptyalin (amylase from sahva), pepsin, and others, should not be called ferments, as this term was already in use for yeast cells and other organisms. However, proof was not given for the actual existence of enzymes. EinaHy, in 1897, it was demonstrated that ceU-free yeast extract ("zymase") could convert glucose into ethanol and carbon dioxide in exactiy the same way as viable yeast cells. It took some time before these experiments and deductions were completely understood and accepted by the scientific community. 

Enzyme Nomenclature. The number of enzymes known exceeds two thousand. A system of classification and nomenclature is required to identify them unambiguously. During the nineteenth century, it was the practice to identify enzymes by adding the suffix -in to the name of their source. Names such as papain, ftcin, trypsin, pepsin, etc, are still in use. However, this system does not give any indication of the nature of the reaction catalyzed by the enzyme or the type of substrate involved. 

In some parts of the world, pepsin is also used to clot milk, but it is much less specific and can give rise to a number of degradation products that tend to taste bitter. 

Oncolytic Enzymes. An early report of cancer chemotherapy using an enzyme, pepsin [9001 -75-6] was pubHshed in 1922 (18) its clinical use was surrounded by controversy. 

Enzymes Degrading Macromolecules. Enzymes that degrade macromolecules such as membrane polysaccharides, stmctural and functional proteins, or nucleic acids, have all shown oncolytic activity. Treatment strategies include the treatment of inoperable tumors with pepsin (1) antitumor activity of carboxypeptidase (44) cytotoxicity of ribonudease (45—47) oncolytic activity of neuraminidase (48—52) therapy with neuraminidase of patients with acute myeloid leukemia (53) antitumor activity of proteases (54) and hyaluronidase treatment in the management of human soHd tumors (55). 

Entozyme 18/100 Digestive enymes pancreatin/pepsin/bile salts Robins... 

Pancrease 30/100 pancreatin/pepsin/bile salts McNeil... 

Tlozyme 77/250 pancreatin/pepsin/bile salts Adtia... 

Enzobile 13/100 pancreatic enzyme/ceUulase/pepsin MaUard... 

Kanulase 14/50 amylase / protease /Hpase / pepsin/bile Sandoz... 

Digestalin 3/100 extract/ceUulase/glutamic acid pancreatin/pepsin/papain/activated Vortech... 

Donnazyme 20/100 nyltoloxamine pancreatin/pepsin/homatropine/hyoscyamine/atropin Robins... 

Pepsin [9001-75-6] Mf 31,500(human), 6000(hog) [EC 3.4.23.1]. Rechromatographed on a column of Amberlite CG-50 using a pH gradient prior to use. Crystd from EtOH. [Richmond et al. Biochim Biophys Acta 29 453 I958 Huang and Tang, J Biol Chem 244 1085 1969, 245 2189 1970.]... 

For precipitated protein, buffered solutions containing chaotropic reagents such as 0.1% SDS, 8 M urea, or 6 M guanidine or proteolytic enzymes such as pepsin may be used. However, an extended washing with buffer is required to remove SDS and guanidine. Unexpected elution behavior can occur if these reagents are not removed completely. 

FIGURE 2.16 pH versus enzymatic activity. The activity of enzymes is very sensitive to pH. The pH optimum of an enzyme is one of its most important characteristics. Pepsin is a protein-digesting enzyme active in the gastric fluid. Trypsin is also a proteolytic enzyme, but it acts in the more alkaline milieu of the small intestine. Lysozyme digests the cell walls of bacteria it is found in tears. 

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