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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
Biomolecules and Complex Biological Entities
Published in Simona Badilescu, Muthukumaran Packirisamy, BioMEMS, 2016
Simona Badilescu, Muthukumaran Packirisamy
Many enzymes require coenzymes or cofactors that can be small organic molecules or single metal ions, such as Mg, Zn, Co, Mn, etc. Examples of such enzymes include alcohol dehydrogenase, peroxidase, catalase, xanthine oxidase, etc., which contain sites for binding metal ions. Many of the important dietary vitamins are coenzymes used by certain types of enzymes. Many enzymes can be inhibited by molecules with a similar shape to the substrate, called a competitive inhibitor, that may block the substrate if its concentration is high enough. Inhibitors are compounds that combine with enzymes and prevent an enzyme and substrate from forming the ES complex. They may cause a reduction in the rate of the enzyme-catalyzed reaction or bring about a loss of activity. Two broad classes of enzyme inhibitors generally recognized are reversible and irreversible inhibitors, depending on whether the inhibition can be reversed or not. Heavy metal ions (e.g., mercury and lead) should generally be prevented from coming into contact with enzymes, as they usually cause such irreversible inhibition by binding strongly to the amino acid backbone. It has been shown that enzymes function best within a narrow range of temperature and pH. For human intracellular enzymes the maximum enzyme action was found at 37°C and pH 7.
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]