Hydrolysis peptide

By changing Ser 221 in subtilisin to Ala the reaction rate (both kcat and kcat/Km) is reduced by a factor of about 10 compared with the wild-type enzyme. The Km value and, by inference, the initial binding of substrate are essentially unchanged. This mutation prevents formation of the covalent bond with the substrate and therefore abolishes the reaction mechanism outlined in Figure 11.5. When the Ser 221 to Ala mutant is further mutated by changes of His 64 to Ala or Asp 32 to Ala or both, as expected there is no effect on the catalytic reaction rate, since the reaction mechanism that involves the catalytic triad is no longer in operation. However, the enzyme still has an appreciable catalytic effect peptide hydrolysis is still about 10 -10 times the nonenzymatic rate. Whatever the reaction mechanism... 

Ester hydrolysis Amide hydrolysis Peptide hydrolysis... 

Figure 36 Complexes catalyzing hydrolytic cleavage of peptides, hydrolysis and alcoholysis of nitriles, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various...

Fe ) catalyze ester and peptide hydrolysis as well as phosphoryl transfer proc-It has been stated in the context of short, strong hydrogen bonds, that the... 

Synge, using starch columns, confirmed the presence of valylvaline and identified L-valylglycine in partial hydrolysates. This unexpected finding triggered a good deal of work on the kinetics of peptide hydrolysis in an attempt to develop a rational explanation. 

Peptide hydrolysis by platinum(II) (436) and palladium(II) complexes (437). In the latter case there is selective hydrolysis of the unactivated peptide bond in iV-acetylated L-histidylglycine the hydrolysis rate depends on the steric bulk of the catalyst. 

Figure 12.5 Zinc-hydroxide reaction mechanism for peptide hydrolysis by carboxypeptidase A. (Reprinted with permission from Lipscomb and Strater, 1996. Copyright (1996) American Chemical Society.)...

The finding that the hydrolytic activity of the enzyme is retained after replacement of a tyrosine residue by phenylalanyl challenges the notion that a tyrosine acts as a general acid catalyst in peptide hydrolysis. It has been suggested that either the protonated Glu270 moiety or the zinc-water complex could perform the proton transfer [77]. 

S. A. Bizzozero, H. Dutler, Stereochemical Aspects of Peptide Hydrolysis Catalyzed by Serine Proteases of the Chymotrypsin Type , Bioorg. Chem. 1981, 10, 46 - 62 ... 

In Sect. 6.3, we examined, in some detail, the chemical mechanisms of peptide hydrolysis and showed that, while all are relevant in a pharmaceutical context of production and storage, some are fast enough to shorten the half-life and duration of action of some peptides in the body. However, enzymatic reactions of hydrolysis play a much more important role than non-enzymatic ones in the metabolic degradation of peptides [7] [14][138-141], as discussed in the remainder of this chapter. 

The brush border enzymes in the intestine play a major role in peptide hydrolysis. Thus, both aminopeptidase and endopeptidase activities were detected with [Leu5]enkephalin as the substrate [146],... 

The 20S proteasome is a latent protease owing to the barrier imposed by the a-subunit rings on peptide entry. Consequently, a readily measured activity of the RC is activation of fluorogenic peptide hydrolysis by the 20S proteasome. The extent of activation is generally found to be in the range 3- to 20-fold [63]. Activation is relatively uniform for all three proteasome catalytic subunits and presumably reflects opening by the attached RC of a channel leading to the proteasome s central chamber. 

In addition to the RC there are two protein complexes, REGajS and REGy, and a single polypeptide chain, PA200, that bind the 20S proteasome and stimulate peptide hydrolysis but not protein degradation. Like the RG, proteasome activators bind the ends of the 20 S proteasome and, importantly, they can form mixed or hybrid 26S proteasomes in which one end of the 20S proteasome is associated with a 19S RC and the other is bound to a proteasome activator [147-150]. This latter property raises the possibility that proteasome activators serve to localize the 26S proteasome within eukaryotic cells. 

Thrombin [EC 3.4.21.5], also known as fibrinogenase, catalyzes the hydrolysis of peptide bonds, exhibiting preferential cleavage for the Arg—Gly peptide bond. The enzyme, a member of the peptidase family SI, activates fibrinogen to fibrin and releases fibrinopeptide A and B. Thrombin, formed from prothrombin, is more selective in peptide hydrolysis than trypsin or plasmin. 

Fig. 31. Mechanistic proposal for peptide hydrolysis catalyzed by carboxypeptidase A (Christianson and Lipscomb, 1989). (a) The precatalytic Michaelis complex with substrate carbonyl hydrogen bonded to Arg-127 allows for nucleophilic attack by a water molecule promoted by zinc and assisted by Glu-270 (an outer-sphere C==O Zn interaction is not precluded), (b) Tbe stabilized tetrahedral intermediate collapses, with required proton donation by Glu-270 (Monzingo and Matthews, 1984) Glu-270 may play a bifunctional catalytic role (Schepartz and Breslow, 1987), which results in the product complex (c). [Reprinted with permission from Christianson, D. W., Lipscomb, W. N. (1989) Acc. Chem. Res. 22,62-69. Copyright 1989 American Chemical Society.]...

Idursulfase (Elaprase) is a drug used to treat mucopolysaccharidosis II or Hunter syndrome. It is a lysosomal storage disease caused by iduronate-2-sulfatase deficiency. Idursulfase is a purified form of iduronate-2-sulfatase produced by recombinant DNA technology in a human cell line. The drug provides clinically important benefits to Hunter syndrome patients. After intravenous infusion Idursulfase is eliminated by peptide hydrolysis with an elimination half-life of 45 minutes. The most common adverse events are hypersensitivity reactions, pyrexia, headache and arthralgia. 

Figure 4.7 Fragment condensation of short, prebiotically formed, oligopeptides. The asterisk indicates the catalytically active peptide, which can induce the fragment condensation by reverse peptide hydrolysis n peptides (e.g., ten residues long) react with each other to build ideally 20-peptides, and of these, m react further (to build ideally 40-peptides, of course in practice all possible mixtures may be present), and m are eliminated because of being unusable (e.g., insoluble) under the contingent conditions - and so on.

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