Inhibitors enzyme activity affected

Beyond pharmaceutical screening activity developed on aminothiazoles derivatives, some studies at the molecular level were performed. Thus 2-aminothiazole was shown to inhibit thiamine biosynthesis (941). Nrridazole (419) affects iron metabohsm (850). The dehydrase for 5-aminolevulinic acid of mouse liver is inhibited by 2-amino-4-(iS-hydroxy-ethyl)thiazole (420) (942) (Scheme 239). l-Phenyl-3-(2-thiazolyl)thiourea (421) is a dopamine fS-hydroxylase inhibitor (943). Compound 422 inhibits the enzyme activity of 3, 5 -nucleotide phosphodiesterase (944). The oxalate salt of 423, an analog of levamisole 424 (945) (Scheme 240),... 

The above conclusion is supported by the results shown in figure 4. Just as inhibitors of the 5-HT uptake carrier can antagonize MDMA-induced [ H]5-HT release in vitro, coadministration of MDMA with an uptake inhibitor such as citalopram can completely block the acute depletion of 5-HT. Although citalopram also antagonized the MDMA-induced decrease in TPH activity, there was still a significant loss of enzyme activity when compared to control. This implies that if MDMA requires access to the interior of the nerve terminals to affect TPH activity, it does not require the activity of the uptake carrier to gain entrance. Hence, these results are consistent with the outcome of synaptosomal uptake experiments with [ HJMDMA (Schmidt et al. 1987), which show that MDMA is not actively concentrated by a carrier system. Furthermore, it is apparent that the loss of enzyme activity alone is not sufficient to reduce 5-HT concentrations, but that release via the carrier must occur simultaneously, to deplete the terminal once synthetic capacity is reduced. 

The effects of solution pH on enzyme activity can be particularly informative in defining steps in catalysis that are most affected by interactions with inhibitors. Ionization of different groups on the enzyme can be critical in substrate binding (i.e.,... 

Although substrates may enhance or inhibit their own conversion, as noted in Section 10.4.1, other species may also affect enzyme activity. Inhibitors are compounds that decrease observable enzyme activity, and activators increase activity. The combination of an inhibitor or activator with an enzyme may be irreversible, reversible, or partially... 

On the other hand, combinations between Eqs. (44) and (45) show how, via modification of the electrostatic potential, ionic strength affects Km (and Ky, inhibitor constants), and thus the enzyme activity. 

Many substances can affect metabolic processes by influencing the activity of enzymes. Enzyme inhibitors are particularly important here. A large proportion of medicines act as enzyme inhibitors. Enzyme-kinetic experiments are therefore an important aspect of drug development and testing procedures. Natural metabolites are also involved in regulatory processes as inhibitors (see p.ll4). 

Phenolic compounds naturally occurring in plants have induced many physiological responses that duplicate those reported for ozone and/or peroxyacetylnitrate (PAN). Chlorogenic acid is a competitive inhibitor of lAA-oxidase (35) and plant growth is adversely affected by increased concentrations of auxins (36). Concentrations of chlorogenic acid are increased in tobacco tissue exposed to ozone ( ) Phenols inhibit ATP synthesis (37), oxidative phosphorylation ( ) and SH enzyme activity (27) they increase respiration (38), reduce CO2 fixation (22), modify both membrane permeability (40) and oxidation rate of reduced NADH... 

Rates of enzyme reactions are often affected by the presence of various chemicals and ions. Enzyme inhibitors combine, either reversibly or irreversibly, with enzymes and cause a decrease in enzyme activity. Effectors control enzyme reactions by combining with the regulatory site(s) of enzymes. There are several mechanisms of reversible inhibition and for the control of enzyme reactions. 

Most, if not all, milks contain sufficient amounts of lipase to cause rancidity. However, in practice, lipolysis does not occur in milk because the substrate (triglycerides) and enzymes are well partitioned and a multiplicity of factors affect enzyme activity. Unlike most enzymatic reactions, lipolysis takes place at an oil-water interface. This rather unique situation gives rise to variables not ordinarily encountered in enzyme reactions. Factors such as the amount of surface area available, the permeability of the emulsion, the type of glyceride employed, the physical state of the substrate (complete solid, complete liquid, or liquid-solid), and the degree of agitation of the reaction medium must be taken into account for the results to be meaningful. Other variables common to all enzymatic reactions—such as pH, temperature, the presence of inhibitors and activators, the concentration of the enzyme and substrate, light, and the duration of the incubation period—will affect the activity and the subsequent interpretation of the results. 

Where rather detailed studies have been made, it has been found that the actions of inhibitors on enzymic activities often are quite significantly affected by such factors as reaction pH and the presence of... 

Enzyme immobilization has been reported to improve the thermal stability of enzymes (1,2) and may also affect binding of substrates and inhibitors to the enzyme, thereby affecting the Michaelis constant and enzyme inhibition. Several previous studies have considered the advantages of immobilized enzymes with soluble substrates, and a few studies have also investigated the properties of immobilized enzymes with insoluble substrates. The main objective of the present work was to establish the effect of immobilization on the thermal stability of these enzymes, so that they may be used at elevated temperatures without significant activity loss. The immobilization conditions were varied, and their effect on the performance of the immobilized enzymes was analyzed with reference to their physiochemical and structural properties. 

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