Competive inhibitors

In an attempt to further elucidate the mechanism of this process, these workers monitored the reaction between propiophenone enolsilane and fumaroylimide by in situ infrared (IR) spectroscopy, Scheme 25 (240). In the absence of alcoholic additives, the accumulation of an intermediate is observed prior to appearance of product. When i-PrOH is introduced, immediate decomposition of the intermediate occurs with concomitant formation of product. Evans suggests that the intermediate observed in this reaction is dihydropyran (374). Indeed, this reaction may be viewed as a hetero-Diels-Alder cycloaddition followed by alcohol induced decomposition to the desired Michael adduct. That 374 may be acting as a competent inhibitor was suggested by an observed rate reduction when this reaction was conducted in the presence of IV-methyloxazolidinone. 

Identification of all packing defects - dehydrons - targetable by ATP competing inhibitors for each human kinase. 

Introduction of a competing inhibitor results in the formation of two different receptor complexes. The inhibitor will displace a certain amoimt of the labeled ligand, depending on its concentration and own affinity to the... 

Inhibitors and retarders differ in the extent to which they interfere with polymerization, and not in their essential activity. An inhibitor is defined as a substance which blocks polymerization completely until it is either removed or consumed. Thus failure to totally eliminate an inhibitor from purified monomer will result in an induction period in which the inhibitor is first converted to an inert form before polymerization can begin. A retarder is less efficient and merely slows down the polymerization process by competing for radicals. 

Reversible inhibition is characterized by an equiUbrium between enzyme and inhibitor. Many reversible inhibitors are substrate analogues, and bear a close relationship to the normal substrate. When the inhibitor and the substrate compete for the same site on the enzyme, the inhibition is called competitive inhibition. In addition to the reaction described in equation 1, the competing reaction described in equation 3 proceeds when a competitive inhibitor I is added to the reaction solution. 

A competitive inhibitor biads to the same enzyme form as the substrate, competing for the same site, such that the inhibitor and substrate prevent one another from binding. This may be represented as follows -Compet twe inhibition... 

Unlike a competitive inhibitor, a noncompetitive inhibitor does not compete with the substrate for the binding site, siace the inhibitor and substrate can biad to the enzyme either iadepeadeatiy or smi A. 2in.eou y.]S1oncompetitive inhibition... 

Like a noncompetitive inhibitor, an uncompetitive inhibitor does not compete with the substrate since it binds to the enzyme—substrate complex but not to the free enzyme. Uncompetitive inhibition... 

The basic kinetic properties of this allosteric enzyme are clearly explained by combining Monod s theory and these structural results. The tetrameric enzyme exists in equilibrium between a catalytically active R state and an inactive T state. There is a difference in the tertiary structure of the subunits in these two states, which is closely linked to a difference in the quaternary structure of the molecule. The substrate F6P binds preferentially to the R state, thereby shifting the equilibrium to that state. Since the mechanism is concerted, binding of one F6P to the first subunit provides an additional three subunits in the R state, hence the cooperativity of F6P binding and catalysis. ATP binds to both states, so there is no shift in the equilibrium and hence there is no cooperativity of ATP binding. The inhibitor PEP preferentially binds to the effector binding site of molecules in the T state and as a result the equilibrium is shifted to the inactive state. By contrast the activator ADP preferentially binds to the effector site of molecules in the R state and as a result shifts the equilibrium to the R state with its four available, catalytically competent, active sites per molecule. 

The regioselectivity of addition of Itydrogen bromide to alkenes can be complicated if a free-radical chain addition occurs in competition with the ionic addition. The free-radical reaction is readily initiated by peroxidic impurities or by light and leads to the anti-Markownikoff addition product. The mechanism of this reaction will be considered more fully in Chapter 12. Conditions that minimize the competing radical addition include use of high-purity alkene and solvent, exclusion of light, and addition of free-radical inhibitors. ... 

The three most common types of inhibitors in enzymatic reactions are competitive, non-competitive, and uncompetitive. Competitive inliibition occurs when tlie substrate and inhibitor have similar molecules that compete for the identical site on the enzyme. Non-competitive inhibition results in enzymes containing at least two different types of sites. The inhibitor attaches to only one type of site and the substrate only to the other. Uncompetitive inhibition occurs when the inhibitor deactivates the enzyme substrate complex. The effect of an inhibitor is determined by measuring the enzyme velocity at various... 

L-NAME (N-nitro-L-arginine methyl ester), like L-NMMA, is a structural analogue of L-arginine and competes with L-arginine for NO-synthase, which uses L-arginine as a substrate for the formation of NO. L-NMMA and L-NAME are very effective NO-synthesis inhibitors, both in vitro and in vivo. 

Espeseth AS, Felock P, Wolfe A, Witmer M, Grobler J, Anthony N, Egbertson M, Melamed JY, Young S, Hamill T et al (2000) HlV-1 integrase inhibitors that compete with the target DNA substrate define a unique strand transfer conformation for integrase. Proc Natl Acad Sci USA 97 11244-11249... 

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