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Enzyme Kinetics and Drugs as Enzyme Inhibitors
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Competitive inhibitors are of widespread clinical use as therapeutics. In case of competitive inhibition, the active site of the enzyme binds either the substrate (ES) or the inhibitor (EI) but not both inhibitor and substrate (ESI). Competitive inhibitors show structural similarities with the natural substrate and are recognized by the active site. Competitive inhibition can be reversed by increasing the substrate concentration. Product inhibition can be looked at as a special kind of competitive inhibition; for example, hexokinase binds its substrate glucose as well as the product glucose-6-phosphate so that an accumulation of this metabolite is avoided. The rate equation for competitive inhibition is vi=Vmax⋅(S)KM(1+(I)KI)+(S)
Enzymatic Reaction Kinetics
Published in Debabrata Das, Debayan Das, Biochemical Engineering, 2019
A competitive inhibitor has strong structural resemblance to the substrate, and the substrate and the inhibitor compete for the same active site of the enzyme. The formation of an enzyme–inhibitor complex reduces the available surface area of the enzyme for interaction with the substrate and that largely decreases the reaction rate. A competitive inhibitor normally combines reversibly with an enzyme. Therefore, the effect of the inhibitor can be minimized by increasing the substrate concentration, unless the substrate concentration is greater than the concentration at which the substrate itself inhibits the reaction. The mechanism of competitive inhibition can be expressed as follows: () E+S↔k2k1ES () E+I↔k4k3EI () ES→k5E+P
Biodegradation of Phenol
Published in Donald L. Wise, Debra J. Trantolo, Remediation of Hazardous Waste Contaminated Soils, 2018
C. Vipulanandan, S. Wang, S. Krishnan
The inhibition of bacterial growth is often due to the inhibition of enzyme systems. An enzyme inhibitor reduces the rate of an enzymatically catalyzed reaction by binding either with the free enzyme and/or with the enzyme-substrate complex. Three types of models are frequently used to explain cell growth inhibition: competitive, noncompetitive, and uncompetitive. Competitive inhibition occurs when a substrate competes with another substrate for a site on either the cell or the enzyme. Noncompetitive inhibition occurs when the inhibitor can combine with both the free cell or enzyme and the cell/enzyme–substrate complex. An uncompetitive inhibitor binds with the cell/enzyme-substrate complex, which cannot undergo further reaction to yield product. Uncompetitive inhibition is believed to be the most frequently responsible mechanism for cell growth inhibition.
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]
Catalytic and thermodynamic properties of β-glucosidases produced by Lichtheimia corymbifera and Byssochlamys spectabilis
Published in Preparative Biochemistry and Biotechnology, 2018
Tobias Pereira de Morais, Paula Mirella Gomes Barbosa, Nayara Fernanda Lisboa Garcia, Nathália Gonsales da Rosa-Garzon, Gustavo Graciano Fonseca, Marcelo Fossa da Paz, Hamilton Cabral, Rodrigo Simões Ribeiro Leite
β-Glucosidases produced by L. corymbifera and B. spectabilis showed reversibility to glucose inhibition when the substrate concentration was increased to match the inhibitor concentration (Table 3). The reversibility of inhibition by increasing substrate concentration indicates competitive inhibition.[6,8] In this type of inhibition, the inhibitor (glucose) and the substrate compete for the same binding site on the enzyme, the active site. The increase in the substrate concentration favors its binding to the active site, reversing the inhibitory effect generated by glucose.[3]