Calculation of inhibitor Ki and inhibitor type from the concentration of inhibitor for 50% inhibition for Michaelis-Menten enzymes |
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| Authors: | R B Brandt J E Laux S W Yates |
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| Institution: | 1. Department of Biochemistry, Medical College of Virginia/Virginia Commonwealth University, Richmond, Virginia 23298 USA;2. Massey Cancer Center, Medical College of Virginia/Virginia Commonwealth University, Richmond, Virginia 23298 USA;1. Nuclear Physics Laboratory, Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece;2. Department of Archaeometry and Physicochemical Measurements, R.C. ‘Athena’, P.O. Box 159, Kimmeria University Campus, 67100 Xanthi, Greece;1. Center for Protein Studies, Faculty of Biology, University of Havana, Cuba;2. Molécules de Communication et Adaptation des Microorganismes, (MCAM, UMR 7245), Muséum National Histoire Naturelle, Sorbonne Universités, CNRS, CP 52, 57 Rue Cuvier, 75005, Paris, France;3. Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Ave Universidad 2001, Cuernavaca, Morelos, Mexico;4. Instituto de Oncología y Radiobiología, Habana, Cuba;1. Center of Bioinformatics, University of Allahabad, Allahabad 211002, India;2. Department of Biochemistry, University of Allahabad, Allahabad 211002, India;6. Institute fof Glycomics, Griffith University, Gold Coast Campus, Queensland 4222, Australia |
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| Abstract: | The use of I50 (concentration of inhibitor required for 50% inhibition) for enzyme or drug studies has the disadvantage of not allowing easy comparison among data from different laboratories or under different substrate conditions. Modifications of the Michaelis-Menten equation for treatment of inhibitors can allow both the determination of the type of inhibition (competitive, noncompetitive, and uncompetitive) and the Ki for the inhibitor. For competitive and uncompetitive inhibitors when the assay conditions are S] = Km, then Ki = I50/2. For different conditions of S] there is a divergence between competitive and uncompetitive inhibitors that may be used to identify the type of inhibitor. The equation for Ki also differs. For noncompetitive inhibitors the Ki = I50 and this relationship is valid with changing S]. The equations developed require a single substrate, reversible-type inhibitors, and kinetics of the Michaelis-Menten type. Examples of the use of the equations are illustrated with experimental data from scientific publications. |
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