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Irreversible inhibition

Methods based on the inhibitory effect of the analyte and the use of an enzyme thermistor have primarily been applied to environmental samples and typically involve measuring the inhibitory effect of a pollutant on an enzyme or on the metabolism of appropriate cells [162]. The inhibiting effect of urease was used to develop methods for the determination of heavy metals such as Hg(II), Cu(II) and Ag(I) by use of the enzyme immobilized on CPG. For this purpose, the response obtained for a 0.5-mL standard pulse of urea in phosphate buffer at a flow-rate of 1 mL/min was recorded, after which 0.5 mL of sample was injected. A new 0.5-mL pulse of urea was injected 30 s after the sample pulse (accurate timing was essential) and the response compared with that of the non-inhibited peak. After a sample was run, the initial response could be restored by washing the column with 0.1-0.3 M Nal plus 50 mM EDTA for 3 min. Under these conditions, 50% inhibition (half the initial response) was obtained for a 0.5-mL pulse of 0.04-0.05 mM Hg(II) or Ag(I), or 0.3 mM Cu(II). In some cases, the enzyme was inhibited irreversibly. In this situation, a reversible enzyme immobilization technique... [Pg.140]

Irreversible Inhibition of an Enzyme Many enzymes are inhibited irreversibly by heavy metal ions such as Hg2+, Cu2+, or Ag+, which can react with essential sulfhydryl groups to form mercaptides ... [Pg.236]

A closely related E. coli protein is a 79-kDa multifunctional enzyme that catalyzes four different reactions of fatty acid oxidation (Chapter 17). The amino-terminal region contains the enoyl hydratase activity.32 A quite different enzyme catalyzes dehydration of thioesters of (3-hydroxyacids such as 3-hydroxydecanoyl-acyl carrier protein (see Eq. 21-2) to both form and isomerize enoyl-ACP derivatives during synthesis of unsaturated fatty acids by E. coli. Again, a glutamate side chain is the catalytic base but an imidazole group of histidine has also been implicated.33 This enzyme is inhibited irreversibly by the N-acetylcysteamine thioester of 3-decynoic acids (Eq. 13-8). This was one of the first enzyme-activated inhibitors to be studied.34... [Pg.682]

Irreversible inhibitors often provide clues to the nature of the active site. Enzymes that are inhibited by iodo-acetamide, for example, frequently have a cysteine in the active site, and the cysteinyl sulfhydryl group often plays an essential role in the catalytic mechanism (fig. 7.18). An example is glyceraldehyde 3-phosphate dehydrogenase, in which the catalytic mechanism begins with a reaction of the cysteine with the aldehyde substrate (see fig. 12.21). As we discuss in chapter 8, trypsin and many related proteolytic enzymes are inhibited irreversibly by diisopropyl-fluorophosphate (fig. 7.18), which reacts with a critical serine residue in the active site. [Pg.150]

A newer class of MAO inhibitors, which has entered clinical practice for the treatment of depression, is known as reversible inhibitors of MAO A (RIMAs). This is a very welcome development in new drug therapeutics for depression, because it has the potential of making MAO A inhibition for the treatment of depression much safer. That is, the suicide inhibitors are associated with the dangerous hypertensive episodes mentioned above, which are caused when patients eat food rich in tyramine (such as cheese). This so-called cheese reaction occurs when the tyramine in the diet releases norepinephrine and other sympathomimetic amines (Fig. 5—23). When MAO is inhibited irreversibly, the levels of these amines rise to a dangerous level... [Pg.215]

Thrombin inhibition Irreversible Reversible Irreversible Reversible... [Pg.97]

Ketone 2 and its metabolite chloro-acetone (16) are alkylating agents. This property is of special importance, when the substrate is being reduced stereoselectively by reductases with an essential sulfhydryl function. Because the sulfhydryl groups are inhibited irreversibly by alkylation [69], stereoisomer distribution in the product is considerably affected. [Pg.74]

These inhibitors would be classified as anti-juvenile hormones and could be expected to show selective action on insects as a class. Such analogs are by no means just around the corner since at least two important properties that they should possess may be difficult to build into small organic molecules suitable for pest control. These properties are the ability to withstand general metabolic inactivation while retaining the ability to inhibit irreversibly the target enzymes of the corpus allatum and the property to accumulate selectively in corpora allata, a physically small target, so as to offset dilution in the general body cavity. [Pg.198]

The N-hydroxy amino acid derivatives are likely to be applicable to other metalloproteases. Thermolysin is inhibited irreversibly at pH 7.2 by ClCH2CO-DL-HOLeu-OCH3 where HOLeu is N-hydroxyleucine (47). The inhibition reaction involves coordination of the hydroxamic acid functional group to the active-site zinc atom of the enzyme. This then places the chloroacetyl group adjacent to Glu-143, an essential catalytic residue of thermolysin (see Figure 9). An ester linkage is formed and the enzyme is inactivated irreversibly. This reagent also inactivated two neutral metalloproteases from B. subtilis, but reacted only very slowly with carboxypeptidase A (t1/2 > 3 d). [Pg.358]

This article describes various approaches to inhibition of enzyme catalysis. Reversible inhibition includes competitive, uncompetitive, mixed inhibition, noncompetitive inhibition, transition state, and slow tight-binding inhibition. Irreversible inhibition approaches include affinity labeling and mechanism-based enzyme inhibition. The kinetics of the various inhibition approaches are summarized, and examples of each type of Inhibition are presented. [Pg.436]

The biochemical properties of chloroquine and related anti-malarials have been exeonined further. In addition to its inhibition of the biosynthesis of sulfated mucopolysaccharides, chloroquine inhibits irreversibly an autolytic enzyme from bovine cartilage and a rat skin collagenase (at 10 mM). Like hydrocortisone, it inhibits chemotaocis of leukocytes and, to a lesser extent, the phagocytosis process.It also stabilizes lysosomal membranes in vitro. Potential "anti-degenerative" activity is clearly suggested by these properties, but unfortunately the well-known retinopathic effect is further complicated by a delayed symptom. [Pg.223]

Receptor tyrosine kinases (RTKs) are activated (phosphorylated) by inhibition of a negatively regulating phosphatase upon treatment with UV (A, B, or C), hydrogen peroxide, or iodoacetamide. The phosphatase activity, (i.e., dephosphorylation and inactivation of RTKs) is restored upon the addition of thiol-regenerating agents, if not inhibited irreversibly by iodoacetamide [20]. H2O2 not only inactivates membrane-bound phosphatases but also diminishes cytosolic general protein tyrosine phosphatase activity in mouse fibroblasts [21]. Further, the activation of JNK by sodium arsenite, which is reactive towards thiols (especially vicinal dithiols), is by inactivation of a JNK phosphatase [22]. [Pg.208]

We showed ear11er(18) that the presence of Harman or Norharman did not interfere the reversible noncovalent DNA binding for Trp-P-2, but inhibited irreversible covalent DNA binding in vitro upon the metabolic activation by the crude microsomal fraction isolated from 3-MC pretreated rat livers. [Pg.112]

The degree of steric encumbrance is illustrated by the rates of metallation and oxidation of the various isomers. The adjacent cis-linked isomer 248c has one face unhindered and is easily metallated. In contrast the other isomers, where both faces are hindered, undergo iron insertion reluctantly. While not preventing ligation of nitrogenous bases or diatomic molecules, the chains do inhibit irreversible oxidation at room temperature. For the four-coordinate iron(II) cross trans-linked isomer 248a the t a for oxidation to the hematin derivative Fe (P)OH is 1.5-10.5 minutes compared to 7-54 seconds for oxidation of the less hindered isomers to the p-oxo complex. Similarly, in toluene at 25 °C under O2 (1 atm), t]/2 for oxidation of the six-coordinate iron(II) complex is 11-25 min for the cross trans-linked isomer compared to 1.5-12 min for the other two isomers ... [Pg.193]

Meyer RE, Shan S, DeAngelo J, Dodge RK, Bonaventura J, Ong ET, Dewhirst MW. Nitric oxide synthase inhibition irreversibly decreases perfusion in the R3230Ac rat mammary adenocarcinoma. Br J Cancer 1995 71 1169-1174. [Pg.116]


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Acetylcholinesterase inhibition irreversible

Amino acid decarboxylases, irreversible inhibition

Enzyme inhibition, active-site-directed irreversible

Enzyme inhibition/inhibitors irreversible

Enzyme irreversible-inhibition studies

Fluorination irreversible inhibition

Inhibition slowly reversible/irreversible inhibitors

Irreversible enzyme inhibition method

Irreversible inhibition inhibitors

Irreversible inhibition, enzyme

Irreversible inhibition, enzyme catalysis

Irreversible inhibition, of enzymes

Irreversible-inhibition studies

Mechanism-based inhibition irreversible

Product analogs, irreversible inhibition

Simple Irreversible Inhibition in the Presence of Substrate

Simple irreversible inhibition

Simple irreversible inhibition time-dependent

Substrates simple irreversible enzyme inhibition

Time-Dependent Simple Irreversible Inhibition in the Presence of Substrate

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