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Pepsin substrates

Pepsin hydrolyzes proteins to products that are not precipitated by the conventional protein precipitants, such as trichloroacetic acid. Very little of the protein is converted to free amino acids, as many peptide bonds are not attacked by pepsin. Not all of the structural requirements for pepsin substrates have yet been determined. Studies with synthetic peptides have shown that the reaction rate is increased when an aromatic amino acid contributes the N of the amide, and is fastest when both amino acids of the peptide to be split are aromatic. In the latter case the pH optimum is near 2, as it is when many protein substrates are used. Many of the other synthetic substrates are split more rapidly near pH 4. [Pg.27]

The data presented so far provides no information about the relative rate at which pepsin hydrolyzes various peptide bonds. It would be important, therefore, to compare these results with the hydrolytic kinetics of some of their bonds in low-molecular-weight peptide substrates. Despite the fact that much information has been obtained in kinetic studies of pepsin using synthetic substrates (3), there always seems to be a need for new highly soluble and easily available peptide substrates of pepsin. We have synthesized and studied a new type of pepsin substrate (Table II) whose solubility was improved as a result of the introduction into the COOH-termini of these peptides an y-aminopropylmorpholine group. The p-nitro-phenylalanine residue can be placed into positions Pi (6), and Pi of the substrate, allowing the kinetics to be studied spectrophoto-metrically. [Pg.182]

A series of Tyr-containing peptides that were not split by cathepsin D are listed in Table II. Typical pepsin substrates such as Z-Clu-Tyr and Z-His-Tyr-OMe were not cleaved by cathepsin D. It was surprising that Tyr-Leu-NH2 and Tyr-Phe-NH2 were not cleaved in view of the cleavage of the related dipeptides noted in Table I, and the known cleavage of NH2-terminal Tyr from the B chain peptide Tyri6-Phe24. It has not yet been possible to find a synthetic Tyr-peptide that is cleaved by cathepsin D on the carboxyl side of Tyr. [Pg.316]

Malak, C. A. (1999). Pepsin as a catalyst for peptide synthesis formation of peptide bonds not typical for pepsin substrate specificity. /. Pept. Res., 53,606-610. [Pg.418]

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. [Pg.471]

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. [Pg.471]

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. [Pg.289]

Mammals, fungi, and higher plants produce a family of proteolytic enzymes known as aspartic proteases. These enzymes are active at acidic (or sometimes neutral) pH, and each possesses two aspartic acid residues at the active site. Aspartic proteases carry out a variety of functions (Table 16.3), including digestion pepsin and ehymosin), lysosomal protein degradation eathepsin D and E), and regulation of blood pressure renin is an aspartic protease involved in the production of an otensin, a hormone that stimulates smooth muscle contraction and reduces excretion of salts and fluid). The aspartic proteases display a variety of substrate specificities, but normally they are most active in the cleavage of peptide bonds between two hydrophobic amino acid residues. The preferred substrates of pepsin, for example, contain aromatic residues on both sides of the peptide bond to be cleaved. [Pg.519]

FIGURE 16.27 A mechanism for the aspartic proteases. In the first step, two concerted proton transfers facilitate nucleophilic attack of water on the substrate carbonyl carbon. In the third step, one aspartate residue (Asp" " in pepsin) accepts a proton from one of the hydroxyl groups of the amine dihydrate, and the other aspartate (Asp" ) donates a proton to the nitrogen of the departing amine. [Pg.521]

Kinetic studies with pepsin have produced bell-shaped curves for a variety of substrate peptides see below, (a). [Pg.525]

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. [Pg.477]

Soya Proteins. Early attempts to make albumen substitutes from soya protein also ran into problems. A bean flavour tended to appear in the finished product. A solution to these problems has been found. Whipping agents based on enzyme modified soy proteins are now available. The advantage of enzymatic modification is that by appropriate choice of enzymes the protein can be modified in a very controlled way. Chemical treatment would be far less specific. In making these materials the manufacturer has control of the substrate and the enzyme, allowing the final product to be almost made to order. The substrates used are oil-free soy flakes or flour or soy protein concentrate or isolate. The enzymes to use are chosen from a combination of pepsin, papain, ficin, trypsin or bacterial proteases. The substrate will be treated with one or more enzymes under carefully controlled conditions. The finished product is then spray dried. [Pg.133]

This aspartic proteinase [EC 3.4.23.22], from the ascomy-cete Endothia parasitica, catalyzes the hydrolysis of proteins with broad specificity similar to that of pepsin A, with preferential action on substrates containing hydrophobic residues at PI and PI. ... [Pg.229]

Figure 1. Schematic representation of the relationships between proposed catalytic and inhibitory mechanisms. A. Postulated general acid-general base catalyzed mechanism for substrate hydrolysis by an aspartyl protease. The water molecule indicated is extensively hydrogen bonded to both aspartic acid residues plus other sites in the active site (see Reference 16 for details). Hydrogen bonds to water are omitted here. B. Kinetic events associated with the inhibition of pepsin by pepstatin. The pro-S hydroxyl group of statine displaces the enzyme immobilized water molecule shown in Figure lA. Variable aspartyl sequence numbers refer to penicillopepsin (pepsin, Rhizopus pepsin), respectively. Figure 1. Schematic representation of the relationships between proposed catalytic and inhibitory mechanisms. A. Postulated general acid-general base catalyzed mechanism for substrate hydrolysis by an aspartyl protease. The water molecule indicated is extensively hydrogen bonded to both aspartic acid residues plus other sites in the active site (see Reference 16 for details). Hydrogen bonds to water are omitted here. B. Kinetic events associated with the inhibition of pepsin by pepstatin. The pro-S hydroxyl group of statine displaces the enzyme immobilized water molecule shown in Figure lA. Variable aspartyl sequence numbers refer to penicillopepsin (pepsin, Rhizopus pepsin), respectively.
We synthesized the ketomethylene, , and hydroxyethylene,8, isosteres of a Leu-Ala dipeptide sequence in order to explore the importance of the two extra atoms in statine relative either to substrate or to the tetrahedral intermediate (Figure 1) in another aspartyl protease system. The compounds were synthesized by the routes outlined in Scheme I. This route was chosen so as to provide steric control at C-2 and C-5 of both 7 and 8 as well as to provide ready access to C-4 labeled analogs. Details of the synthesis have been described else-where.(23.24) Inhibitors were synthesized in which Leu-Ala dipeptide Isosteres replaced either Sta or Sta-Ala in known pepstatin analogs. Inhibition of porcine pepsin was determined using the reported spectrophotometric assay (Table I).(25)... [Pg.220]

In order to establish that the addition process observed for in the active site of pepsin is analogous to that occurring with peptide substrates, the experiments were... [Pg.233]


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See also in sourсe #XX -- [ Pg.9 ]

See also in sourсe #XX -- [ Pg.8 , Pg.9 , Pg.10 , Pg.11 ]




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