title: Enzyme inhibition studies by integrated Michaelis-Menten equation considering simultaneous presence of two inhibitors when one of them is a reaction product.
abstract: To determine initial velocities of enzyme catalyzed reactions without theoretical errors it is necessary to consider the use of the integrated Michaelis-Menten equation. When the reaction product is an inhibitor, this approach is particularly important. Nevertheless, kinetic studies usually involved the evaluation of other inhibitors beyond the reaction product. The occurrence of these situations emphasizes the importance of extending the integrated Michaelis-Menten equation, assuming the simultaneous presence of more than one inhibitor because reaction product is always present. This methodology is illustrated with the reaction catalyzed by alkaline phosphatase inhibited by phosphate (reaction product, inhibitor 1) and urea (inhibitor 2). The approach is explained in a step by step manner using an Excel spreadsheet (available as a template in Appendix). Curve fitting by nonlinear regression was performed with the Solver add-in (Microsoft Office Excel). Discrimination of the kinetic models was carried out based on Akaike information criterion. This work presents a methodology that can be used to develop an automated process, to discriminate in real time the inhibition type and kinetic constants as data (product vs. time) are achieved by the spectrophotometer.
authors.affiliation: Centro de Investigação e de Tecnologias Agro-Ambientais e Biológicas, CITAB, Universidade de Trás-os-Montes e Alto Douro, UTAD, 5000-801 Vila Real, Portugal. Electronic address: bezerra@utad.pt.
authors.forename: Rui M F
authors.initials: RM
authors.lastname: Bezerra
authors.affiliation: Centro de Investigação e de Tecnologias Agro-Ambientais e Biológicas, CITAB, Universidade de Trás-os-Montes e Alto Douro, UTAD, 5000-801 Vila Real, Portugal.
authors.forename: Paula A
authors.initials: PA
authors.lastname: Pinto
authors.affiliation: Centro de Investigação e de Tecnologias Agro-Ambientais e Biológicas, CITAB, Universidade de Trás-os-Montes e Alto Douro, UTAD, 5000-801 Vila Real, Portugal.
authors.forename: Irene
authors.initials: I
authors.lastname: Fraga
authors.affiliation: Centro de Investigação e de Tecnologias Agro-Ambientais e Biológicas, CITAB, Universidade de Trás-os-Montes e Alto Douro, UTAD, 5000-801 Vila Real, Portugal.
authors.forename: Albino A
authors.initials: AA
authors.lastname: Dias
mesh_terms: D002384:Catalysis; D004791:Enzyme Inhibitors / Q000737:chemistry*; D007700:Kinetics
chemical_list: D004791:Enzyme Inhibitors
keywords: Diagnosis of enzyme inhibition; General mechanism kinetics; Integrated Michaelis–Menten equations; Linear inhibition; Two inhibitors