Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Proteolytic reactions

Blood coagulation resulting in the formation of a stable fibrin clot involves a cascade of proteolytic reactions involving the interaction of clotting factors, platelets, and tissue materials. Clotting factors (see table) exist in the blood in inactive form and must be converted to an enzymatic or activated form before the next step in the clotting mechanism can be stimulated. Each factor is stimulated in turn until an insoluble fibrin clot is formed. [Pg.111]

Adler-Nissen, J. 1984. Control of proteolytic reactions and the level of bittnerness in protein hydrolysis processes. J. Chem. Technol. Biotech-nol. 34B 215. [Pg.139]

The blood coagulation cascade. Each of the curved red arrows represents a proteolytic reaction, in which a protein is cleaved at one or more specific sites. With the exception of fibrinogen, the substrate in each reaction is an inactive zymogen except for fibrin, each product is an active protease that proceeds to cleave another member in the series. Many of the steps also depend on interactions of the proteins with Ca2+ ions and phospholipids. The cascade starts when factor XII and prekallikrein come into contact with materials that are released or exposed in injured tissue. (The exact nature of these materials is still not fully clear.) When thrombin cleaves fibrinogen at several points, the trimmed protein (fibrin) polymerizes to form a clot. [Pg.177]

Proteins are informational macromolecules, the ultimate heirs of the genetic information encoded in the sequence of nucleotide bases within the chromosomes. Each protein is composed of one or more polypeptide chains, and each peptide chain is a linear polymer of amino acids. The order of the amino acids commonly found in the polypeptide chain is determined by the order of nucleotides in the corresponding messenger RNA template. In this chapter we examine four aspects of protein metabolism (fig. 29.1) (1) The process whereby amino acids are ordered and polymerized into polypeptide chains (2) posttranslational alterations in polypeptides, which occur after they are assembled on the ribosome (3) the targeting process whereby proteins move from their site of synthesis to their sites of function and (4) the proteolytic reactions that result in the return of proteins to their starting material, amino acids. [Pg.731]

The principal stages in complement activation. Complement activation occurs exclusively on the microbial cell membrane, where it is triggered by bound antibody or microbial envelope polysaccharides, both of which activate early complement components. Two sets of early components belong to two distinct pathways of complement activation. Activation of each complement system involves a cascade of proteolytic reactions. Each component of the complement system is a proenzyme that is activated by the preceding component of the chain by a limited proteolytic cleavage. The ultimate result of this chain reaction is the development of a complex that attacks the cell membrane. [Pg.841]

About 20 different proteins are included in the complement system Proteins C1-C9, factors B and D, and a series of regulatory proteins. All these proteins are made in the liver, and they circulate freely in the blood and extracellular fluid. Activation of the complement system involves a cascade of proteolytic reactions. In addition to forming membrane attack complexes, the proteolytic fragments released during the activation process promote dilation of blood vessels and the accumulation of phagocytes at the site of infection. [Pg.841]

Antibodies bound to an invading microorganism activate the complement system via the classical pathway. This consists of a cascade of proteolytic reactions leading to the formation of membrane attack complexes on the plasma membrane of the microorganism that cause its lysis. Polysaccharides on the surface of infecting microorganisms can also activate complement directly in the absence of antibody via the alternative pathway. [Pg.97]

There are a vast number of other factors which may be expected to influence the rate of desquamation, for instance, by affecting the rate of proteolytic reactions. pH, water, and ion concentrations, and lipid composition may all be expected to be of importance. Experimental data in this area are very scarce, but some speculations can be made. For instance, the pH dependency of SCCE activity could be of importance. SCCE has optimal activity at pH 7 to 8, but close to half its maximal activity at pH 5.5.36,37 This implies that rather small variations in either direction of the pH of the extracellular space should have effects on the rate of SCCE-mediated protein degradation. In support of this, the rate of spontaneous cell dissociation observed in plantar stratum corneum in vitro showed a marked pH dependency, being highest at neutral to weakly alkaline pH and decreasing at lower pH values.10... [Pg.77]

Thus, rather than trial-and-error development of functionality, it should be possible to design functionality based on the principles of protein structure and function and the specificities of the enzymes used for modification. Use of immobilized exo- and endopeptidases in such technology could be especially attractive for the reasons listed in Table I, particularly since problems associated with autolysis would be eliminated and the extent of proteolytic reactions could be controlled with some precision. [Pg.239]

Some proteolytic enzymes have quite specific actions they attack only a limited number of bonds, involving only particular amino acid residues in a particular sequence. This may lead to the accumulation of well-defined peptides during some enzymic proteolytic reactions in foods. [Pg.82]

Activation of caspases is irreversible, because it involves peptide-bond cleav e. This is unlike most other protein modifications which play a role in cellular regulation. Therefore, proteolysis is involved only in unidirectional, irreversible processes, such as the cell cycle and cell death. But, the possibilities to regulate irreversible reactions are rather limited. In a cascade of proteolytic reactions, the first enzyme in the chain is the most likely point of control. This is the initiator caspase. The signals controlling initiator caspases vary, there are both external and internal signals (Fig. 13.5). Several mechanisms control the irreversible activation of caspases, including phosphorylation, separation, and compartmentalization of pro-caspases and positive and n ative regulators. [Pg.238]

Protein turnover is an important process in living systems (Chapter 23). Proteins that have served their purpose must be degraded so that their constituent amino acids can be recycled for the synthesis of new proteins. Proteins ingested in the diet must be broken down into small peptides and amino acids for absorption in the gut. Furthermore, as described in detail in Chapter 10. proteolytic reactions are important in regulating the activity of certain enzymes and other proteins. [Pg.358]

Fig. 4.6. The proposed arrangement of the RC and h/c, complex in the photosynthetic chain of Rps. sphaeroides. The scheme indicates the reduction of Q to QHj by a pair of RC complexes and the net oxidation of QH2 by two turnovers of the oxidoreductase, as a balance of the oxidation of two quinols and the reduction of one quinone at the site. The proposed sites of proteolytic reactions are also indicated (from Ref. 93). Fig. 4.6. The proposed arrangement of the RC and h/c, complex in the photosynthetic chain of Rps. sphaeroides. The scheme indicates the reduction of Q to QHj by a pair of RC complexes and the net oxidation of QH2 by two turnovers of the oxidoreductase, as a balance of the oxidation of two quinols and the reduction of one quinone at the site. The proposed sites of proteolytic reactions are also indicated (from Ref. 93).
C. Inhibition of the Proteolytic Reactions - The reactions leading to cleaved viral proteins may be blocked in infected cells by at least two distinct strategies. [Pg.247]

The proteolytic reactions of the hemostatic system are neither catalytically efficient nor localized when proteinase and proteinase precursor only are present. The rapid, localized proenzyme activation required for normal hemostatic response occurs only in a complex of proteinase, proteinase precursor, and cofactor protein assembled on the surface of a damaged cell membrane, or in vitro, on the surface of phospholipid bilayers. The catalytic efficiency of an enzyme-catalyzed reaction is expressed by the ratio of the kinetic constants /ic and kJKm). In the activation complexes, kJKm values can be greater than lO M s . With proteinase and proenzyme alone, the kJKm values are only approximately 100 M s and thus the reactions are 10 times less efficient. Expressed in terms of the same amount of product formed in the two situations, a 10 increase represents the difference between requiring 1 minute and about 6 months to form the product ... [Pg.852]

Two mechanisms are involved in the transformation between tautomers one is first order with respect to MDHP concentration, while the other is second order. The first-order reaction involves the solvent in a proteolytic reaction MDHP + Sol Sol H+ + MDHP- (51)... [Pg.72]

The RAS should probably be viewed as a cascade of proteolytic reactions under integrated controls. The cascade produces peptides with pressor- and aldosterone-producing effects.11 The RAS controls blood pressure, blood volume, and electrolytic balance. [Pg.451]

Fig. 12 (a) Cross-sectional view of a microchip, heating element, and thermocouples, (b) Diagram of the microchip used for on-chip proteolytic reactions, separations, and post-column labeling for generating fluorescent moieties. The fluid reservoirs are (1) substrate, (2) enzyme, (i) buffer, (4) sample waste, (5) NDA, and (6) waste. Reproduced from [134]... [Pg.284]

The enzyme-catalyzed hydrolysis of a particular peptide bond is determined by two major factors, the susceptibility of that bond to the specific proteinase and the flexibility of the protein chain in the region of the bond. Thus a globular protein undergoes frequent fluctuations, and the sites of the peptide chains of highest mobility are the most susceptible to proteolytic reactions. On the other site, the... [Pg.134]

Lozano and Combes [65,69] proposed an overall interpretation of all proteolytic reactions hydrolysis, transpeptidation, and condensation, as a general mechanism of the plastein reaction. [Pg.136]

Proteolytic reactions take place in general in aqueous media, with the equilibrium in the direction of hydrolysis [87]. However, with decreased water activity, the equilibrium of the reaction is shifted toward synthetic reactions [74]. The use of organic media provides a potentially useful approach to the enzymatic modification of food protein. It has been already established that proteinases are active in organic media. They catalyze ester synthesis or aminolysis by synthesizing new peptide bonds preferentially to hydrolysis. [Pg.140]

A number of factors, including tissue damage, allergic reactions, viral infections, and other inflammatory events, activate a series of proteolytic reactions that generate bradykinin and kallidin in tissues. These peptides contribute to inflammatory responses as autacoids that act locally to produce pain, vasodilation, and increased vascular permeability. Much of their activity is due to stimulation of the release of potent mediators such as prostaglandins, NO, or endothelium-derived hyperpolarizing factor (EDHF). [Pg.411]


See other pages where Proteolytic reactions is mentioned: [Pg.302]    [Pg.455]    [Pg.319]    [Pg.754]    [Pg.302]    [Pg.228]    [Pg.761]    [Pg.18]    [Pg.137]    [Pg.63]    [Pg.106]    [Pg.66]    [Pg.113]    [Pg.808]    [Pg.850]    [Pg.133]    [Pg.273]    [Pg.1833]    [Pg.292]    [Pg.134]    [Pg.63]    [Pg.816]    [Pg.834]    [Pg.496]    [Pg.1962]    [Pg.136]    [Pg.229]   


SEARCH



Proteolytic

Proteolytic reaction mixed

© 2024 chempedia.info