Reversible inhibition, of enzymes

If the inhibitor is found to bind rapidly (linear progress curves) and dissociate rapidly (rapid recovery of activity upon dilution) from its target enzyme, then one can proceed to analyze its inhibition modality and affinity by classical methods. The modes of reversible inhibition of enzymes were described in Chapter 3. In the next section of this chapter we will describe convenient methods for determining reversible inhibition modality of lead compounds and lead analogues during compound optimization (i.e., SAR) studies. 

Reversible Inhibition of Enzymes for Optical Detection of Chemical Analytes... 

Elucidating Mechanisms for the Inhibition of Enzyme Catalysis An inhibitor interacts with an enzyme in a manner that decreases the enzyme s catalytic efficiency. Examples of inhibitors include some drugs and poisons. Irreversible inhibitors covalently bind to the enzyme s active site, producing a permanent loss in catalytic efficiency even when the inhibitor s concentration is decreased. Reversible inhibitors form noncovalent complexes with the enzyme, thereby causing a temporary de-... 

Herbicidal Inhibition of Enzymes. The Hst of known en2yme inhibitors contains five principal categories group-specific reagents substrate or ground-state analogues, ie, rapidly reversible inhibitors affinity and photo-affinity labels suicide substrate, or inhibitors and transition-state, or reaction-intermediate, analogues, ie, slowly reversible inhibitors (106). 

In addition to its broad-spectrum biocidal activity, triclosan (22) displays reversible inhibition of E. coli Fabl with a picomolar K, for binding the enzyme-cofactor complex [4]. Triclosan entry results in the reordering of a loop of amino acids close to the active site, making it a slow, tight-binding inhibitor [41]. 

Purified preparations of calf intestinal AP maintained in solution are usually stored in the presence of a stabilizer, which is typically 3 M NaCl. The enzyme also may be lyophilized, but it may experience activity loss with each freeze-thaw cycle. AP is not stable under acidic conditions. Lowering the pH of an AP solution to 4.5 reversibly inhibits the enzyme. It is recommended that all handling, storage, and use of AP be done under conditions >pH 7.0 to maintain the highest possible catalytic activity. 

Showdomycin inhibits synthesis of nucleic acid. Thiols, such as cysteine and glutathione (among other compounds), reverse this inhibition, and it is considered that the interaction of the maleimide moiety with sulfhydryl groups within the cell or in the membrane may be responsible for the selective inhibition of enzymes by show-... 

Binding of a reversible inhibitor to an enzyme is rapidly reversible and thus bound and unbound enzymes are in equilibrium. Binding of the inhibitor can be to the active site, or to a cofactor, or to some other site on the protein leading to allosteric inhibition of enzyme activity. The degree of inhibition caused by a reversible inhibitor is not time-dependent the final level of inhibition is reached almost instantaneously, on addition of inhibitor to an enzyme or enzyme-substrate mixture. 

Reversible inhibition of an enzyme by an inhibitor binding to the enzyme whether or not the substrate is bound at the active site . A noncompetitive inhibitor binds at a site that is distinct from the active site, and saturating levels of substrate cannot completely remove the inhibitory influence of this agent. 

This term usually applies to reversible inhibition of an enzyme-catalyzed reaction in which nonlinearity is detected (a) in a double-reciprocal plot (i.e., 1/v versus 1/ [S]) in the presence of different, constant concentrations of inhibitor or (b) in replots of slope or intercept values obtained from primary plots of 1/v versus 1/[S]). Nonline-... 

It acts peripherally by inhibiting the synthesis of prostaglandins by reversible inhibition of cyclooxygenase. Inhibition of the migration of leukocytes to an inflammatory site and inhibition of the release of lysosomal enzymes may also be involved in the antiinflammatory action. 

Reversible inhibition of an enzyme is competitive, uncompetitive, or mixed. Competitive inhibitors compete with substrate by binding reversibly to the active site, but they are not transformed by the enzyme. Uncompetitive inhibitors bind only to the ES complex, at a site distinct from the active site. Mixed inhibitors bind to either E or ES, again at a site distinct from the active site. In irreversible inhibition an inhibitor binds permanently to an active site by forming a covalent bond or a veiy stable noncovalent interaction. 

The action of most enzymes is inhibited by many substances. Inhibition is often specific, and studies of the relationship between inhibitor structure and activity have been important to the development of our concepts of active sites and of complementarity of surfaces of biomolecules. Inhibition of enzymes is also the basis of the action of a very large fraction of important drugs. Inhibition may be reversible or irreversible, the latter leading to permanent inactivation of the enzyme. Often, but not always, irreversible inhibition is preceded by reversible binding of the inhibitor at a complementary site on the enzyme surface. 

An adjacent tnfluoromethyl group sharply increases the electrophilic character of the carbonyl carbon Compounds that readily form hydrates and hemiacetals show a time-dependent reversible inhibition of the enzyme acetylcholinesterase (equation 2), in which the tight complex makes inhibition only partially reversible [75] In comparison with a nonfluonnated analogue, several aliphatic ketones flanked by CF3 and CF2 groups, are exceptionally potent reversible inhibitors of acetylcholinesterase, as documented by comparison of inhibition constants Kv shown in equation 3 [76]... 

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