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Metabolism
Published in Markus W. Covert, Fundamentals of Systems Biology, 2017
There are other ways to regulate enzyme activity at much faster times-cales, four of which are shown in Figure 9.10. During substrate inhibition, excess substrate itself prevents effective enzyme–substrate interaction. In some cases, an inhibitor molecule can form a complex with the enzyme to prevent optimal substrate binding. Direct binding between the inhibitor and the enzyme’s active site is called competitive inhibition. The inhibitor may also act by binding a different part of the enzyme, thereby triggering a structural change in the enzyme that changes the active site, a process known as noncompetitive inhibition. A final type of regulation is called uncompetitive inhibition, when the inhibitor binds the enzyme–substrate complex and prevents release of the substrate from the enzyme.
Enzyme Kinetics and Drugs as Enzyme Inhibitors
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
In contrast to competitive inhibitor molecules, non-competitive inhibitors show no distinct similarity to the structure of the substrate molecule to be converted. They do not bind to the active but to a different (sometimes named allosteric) site (S and I can bind to the enzyme molecule simultaneously) of the enzyme which is accompanied by a distortion of the active site; altering the conformation of the catalytic residues within the active site leads to a decrease of the rate of the chemical reaction catalyzed by the enzyme; other than in case of competitive inhibition this effect cannot be reverted, by increasing the substrate concentration. Binding of a non-competitive inhibitor molecule decreases Vmax to an apparent Vmax (due to a reduction of the amount of active enzyme) whereas the KM-value remains unchanged. The kinetics of non-competitive inhibition are rather complex; for the simplest case of a linear non-competitive inhibition where the substrate does not affect inhibitor-binding the following equations (Michaelis–Menten-type equation from which, e.g., a corresponding Lineweaver–Burk plot follows) can be derived (Pelley, 2007). The initial reaction rate is vi=Vmaxapp⋅(S)(S)+KM
Microbial Metabolism
Published in Maria Csuros, Csaba Csuros, Klara Ver, Microbiological Examination of Water and Wastewater, 2018
Maria Csuros, Csaba Csuros, Klara Ver
Noncompetitive inhibition of enzymes occurs when a molecule combines with the enzyme at a site other than the active site. The binding of the molecule causes the enzyme to assume a shape that prevents it from binding with its normal substrate. Noncompetitive, reversible inhibition is the normal way by which metabolic pathways are regulated in cells (see Figure 3.5c).
Production of cellulases by Thermomucor indicae-seudaticae: characterization of a thermophilic β-glucosidase
Published in Preparative Biochemistry and Biotechnology, 2019
Eduardo da Silva Martins, Eleni Gomes, Roberto da Silva, Rodolfo Bizarria Junior
Most microbial β-glucosidases are inhibited by glucose, which becomes a major limitation for the use of these enzymes in industrial processes.[12] High glucose concentrations may directly or indirectly interfere with the binding of the substrate to the activated site, reducing the reaction rate.[32] Inhibition of β-glucosidase produced by T. indicae-seudaticae was completely reversed when the substrate concentration increased but maintained the same glucose concentration. The present work demonstrated that the interaction of the enzyme with the inhibitor is competitive. Competitive inhibition may be reversed by increasing the substrate concentration, which does not occur in noncompetitive inhibition. In competitive inhibition, the inhibitor and the substrate compete for the active site of the enzyme. Thus, increased concentration favors enzyme binding to the substrate, which is reflected in the reversibility of enzymatic inhibition.[20]