Enzyme inhibition complexing agents

Calcium is essential to several steps in the enzyme cascade of the blood clotting process, such as the conversion of prothrombin to thrombin (23). Clotting can be inhibited in stored blood suppHes by addition of complexing agents such as EDTA or citrate which reduce the levels of the free ion, Ca(Il). 

Metallo-enzymes belonging to group 3 naturally show a very broad substrate spectrum including all (3-lactams excqrt monobactams and are not inhibited by clavulanic acid, but by complexing agents, like EDTA. This can only be exploited for diagnostic purposes. 

Protection of the enzyme by a copper ion complexing agent (EDTA) to avoid inhibition by traces of copper ions from the copper catalyst. 

In zinc metalloenzymes. zinc is a selective stoichiometric constituent and is essential for catalytic activity. It is frequently present in numerical correspondence with the number of active enzymatic sites, coenzyme binding sites, or enzyme subunits Removal of zinc results in loss of activity. Inhibition by metal complexing agents is a characteristic feature of zinc metalloenzymes. However, no direct relationship holds between the inhibitory effectiveness of these agents and their affinity for ionic zinc. Although zinc is the only constituent of zinc metalloenzymes in vivo, it can be replaced by other metals m vitro, such as cobalt, nickel, iron, manganese, cadmium, mercury, and lead, as m the case of carboxy-peprida.ses. 

BMost enzymes are sensitive to inhibition by specific agents that interfere with the binding of a substrate at the active site or with conversion of the enzyme-substrate complex into products. Two of the major applications of kinetic measurements are in distinguishing between... 

Bacterial signal peptidase is an example of a known enzyme that could serve as a target for new antibacterial agents [13], Recently, a catalytically active, soluble fragment of signal peptidase from E. coli has been crystallized as a complex with a P-lactam inhibitor [69], This represents a major step in the efforts toward the rational design of inhibitors that can be readily tested for their enzyme inhibition and bacterial growth-inhibition activities. 

Substances which interfere with the specific binding of the substrate to the prosthetic group are specific inhibitors, and differ significantly from agents, which cause nonspecific denaturation of an enzyme (or any protein). Two basic types of inhibitions are recognized competitive inhibition and noncompetitive inhibition. Competitive inhibition is the result of a reversible formation of an enzyme inhibitor complex (El) ... 

The molecular mechanism of enzymatic isomerization is far from being fully understood. In a study of Pseudomonas sp. strain E-3 the similarity between cis-trans isomerase and LOX was hypothesized on the basis of the common inhibition given by antioxidants. However, chelating agents, which do not affect isomerization, also inhibit LOX. A second mechanistic hypothesis was then formulated, consisting of the hydration-dehydration mechanism, similar to the formation of 3-trans-enoyl-CoA from the corresponding cis isomer [28]. Another recent mechanism was proposed based on analysis of carbon isotope fractionation of CTI [25]. Scheme 6.3 shows the proposed mechanism of CTI based on the enzyme-substrate complex as an intermediate, which allows the rotation of the carbon-carbon double bond to occur. 

Generally, the reactivating efficacy of oximes depends on their reactivity and affinity for OPC-inhibited enzyme. Their reactivity is derived from the nucleic activity of oxime anion that is bound on the pyridinium ring (8). Oximes differ from each other by the position of the oxime group on the pyridinium ring only. The reactivity of all available oximes is almost the same because their basic structure is very similar (8). The affinity of oximes for intact enzyme, characterized by dissociation constant of enzyme-reactivator complex (Kdls), and for nerve agent-inhibited enzyme, characterized by dissociation constant of inhibited enzyme-reactivator complex (Kr), is determined by various physicochemical factors such as steric compatibility, electrostatic effects, hydrophobic interactions and by the shape and the size of the whole molecule as well as functional groups (22). 

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