Feedback inhibition cumulative

Cumulative Feedback Inhibition In cumulative feedback inhibition, the end products can inhibit the reaction of the target enzyme separately. Many textbooks erroneously indicate that the cumulative feedback inhibition of E. coli glutamine synthetase involves separate regulatory sites for each feedback inhibitor. See Cumulative Feedback Inhibition... 

Additive Feedback Inhibition This term is restricted to cases in which the end product inhibitors bind to the target enzyme in a mutually exclusive manner and the degrees of inhibition are additive. Extreme care should be exercised when using this term in most cases, the inhibition is really cumulative feedback inhibition. 

CUMULATIVE DISTRIBUTION FUNCTION CUMULATIVE FEEDBACK INHIBITION FEEDBACK INHIBITION CURIE... 

FEEDBACK INHIBITION CUMULATIVE FEEDBACK INHIBITION Feedback inhibitor,... 

The activity of glutamine synthetase is also controlled by reversible covalent modification —the attachment of an AMP unit by a phosphodiester bond to the hydroxyl group of a specific tyrosine residue in each subunit (Figure 24.26). This adenylylated enzyme is less active and more susceptible to cumulative feedback inhibition than is the deadenylylated form. The covalently attached AMP unit is removed from the adenylylated enzyme by phosphorolysis. The attachment of an AMP unit is the final step in an enzymatic cascade that is initiated several steps back by reactants and immediate products in glutamine synthesis. 

Most of the pathways of amino acid biosynthesis are regulated by feedback inhibition, in which the committed step is allosterically inhibited by the final product. Branched pathways require extensive interaction among the branches that includes both negative and positive regulation. The regulation of glutamine synthetase from if. coli is a striking demonstration of cumulative feedback inhibition and of control by a cascade of reversible covalent modifications. 

Cumulative feedback inhibition. Consider the branched pathway above. The first common step (A —> B) is partly inhibited by both of the final products, each acting independently of the other. Suppose that a high level of Y alone decreased the rate of the A B step from 100 to 60 s i and that a high level of Z alone decreased the rate from 100 to 40 s k What would the rate be in the presence of high levels of both Y and Z ... 

Woolfolk, C. A. Stadtman, E. R. (1967). Regulation of glutamine synthetase III. Cumulative feedback inhibition of glutamine synthetase from Escherichia coli. Arch. Biochem. Biophys. 118,736-755. 

Cumulative feedback Inhibition - Eight specific feedback inhibitors, which are either metabolic end products of glutamine (tryptophan, histidine, glucosamine-6-phosphate, carbamoyl phosphate, CTP, or AMP) or indicators of the general status of amino acid metabolism (alanine or glycine), can bind to any of the subunits of the enzyme and at least partially inhibit it. The more inhibitors that bind, the greater the inhibition. 

Cumulative feedback Inhibition - Eight specific feedback inhibitors, which are either metabolic end products of glutamine (tryptophan, histidine, glucosamine-6-phosphate, carbamoyl phosphate, CTP, or... 

All the choices are correct. When all eight compounds are bound to the enzyme, it is almost completely inactive. The control of this enzyme is an excellent example of cumulative feedback inhibition. 

Cumulative The first common step enzyme is inhibited indepently (residual activity, Ai) by each of the end products at saturation cone. The simultaneous presence of the saturation cone, of two or more end products results in the ultimate inhibition such that the total residual activity, A, = HAi. Glutamine synthetase is subject to cumulative feedback inhibition by the end products, carbamyl phosphate, Trp, AMP and CTP. 

A variety of patterns of end-product inhibition have been described [5,69] (1) In enzyme multiplicity inhibition balanced control of an early enzyme of the common part of a branched pathway is obtained because the enzyme is present in the form of several isoenzymes, each specifically inhibited by an end product of one of the branches. (2) In cumulative feedback inhibition an enzyme which mediates the formation of a product used in many pathways is partly inhibited by individual end products of the pathways. Each inhibitor adds its effect to the total inhibition, but the combined effect is less than the sum of the single inhibitions. (3) In concerted feedback inhibition two or more end products are required to act together before any significant inhibition is exhibited. (4) In cooperative feedback inhibition several end products can act as partial inhibitors of an enzyme, but a mixture of two different inhibitors results in greater inhibition than the sum of the individual inhibitions. (5) The term sequential feedback inhibition refers to inhibition of an early enzyme by an intermediate whose accumulation is controlled by inhibition of one or more late pathway enzymes by the end product [71 ]. 

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