Inhibitors feedback phenomena

When the same kind of electrode is introduced in a solution with a high pH (i.e., pH= 10) and a lower substrate concentration (first order kinetics), an oscillation in time of the measured pH inside the membrane spontaneously occurs. This enzyme, which has been extensively studied, does not give oscillation for any conditions of pH and substrate concentration. The period of oscillation is around one-half minute, and the oscillation is abolished by introducing an enzyme inhibitor. The phenomenon can be explained by the autocatalytic effect and by a feedback action of OH- diffusion in from the outside solution. The diffusion of this ion is quicker than the diffusion of the substrate. There is a qualitative agreement between the computer simulation and the experimental results. 

In die metabolic pathway to an amino add several steps are involved. Each step is die result of an enzymatic activity. The key enzymatic activity (usually die first enzyme in the synthesis) is regulated by one of its products (usually die end product, eg die amino add). If die concentration of die amino add is too high die enzymatic activity is decreased by interaction of die inhibitor with the regulatory site of die enzyme (allosteric enzyme). This phenomenon is called feedback inhibition. 

There are many examples of competitive inhibition by compounds that bear no structural relationship to the substrate. The inhibitor is generally an end product or near end product of a metabolic pathway the enzyme is one that catalyzes an early reaction (or a branch-point reaction) in the pathway. The phenomenon is called feedback inhibition. The inhibitor (effector, modulator, or regulator) combines with the enzyme at a position other than the active (substrate) site. The combination of the inhibitor with the enzyme causes a change in the conformation (tertiary or quaternary structure) of the enzyme that distorts the substrate site and thereby prevents the substrate from binding (Model 5). 

The relationship may be negative if the bacterial mediator is toxic. It has been demonstrated that bacteria can produce substances with a high anti-algal activity (Berland et al., 1972a, b, 1973). It is not likely, however, that this phenomenon would actually take place in the natural environment, because of the low concentrations of inhibitors around algal cells. Berland and Maestrini (1969) also showed that the diatom Nitzschia ascicularis, inhibited by antibiotics from different Vibrio and Pseudomonas, in turn activates the synthesis of those inhibitors through a process similar to induction. It is one of the few cases of this type of direct feedback to be observed. ... 

Some comments are required on effectors which are of importance in metabolic and other regulation phenomena. The term allosteric inhibition was introduced by Monod, Changeux Jacob (1963) to explain the discovery of feedback inhibitors, which are competitive with the substrate but not closely structurally related to it. Such inhibitors were called allosteric in contrast to the usual competitive inhibitors which are isosteric with the substrate to fit competitively into the same binding site. Allosteric competitive inhibition occurs at a site (allosteric site) which is separate from the substrate binding sites. Conununication between these separate sites about respective occupancy occurs through conformation changes and these are transmitted through subunit interfaces. The term was extended to the related control phenomenon of allosteric activation, which occurs when a metabolite binds to an allosteric site and decreases the for... 

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