title: Enzyme kinetics: the whole picture reveals hidden meanings.
abstract: The methodology adopted by Michaelis and Menten in 1913 is still routinely used to characterize the catalytic power and selectivity of enzymes. These kinetic measurements must be performed soon after the purified enzyme is mixed with a large excess of substrate. Other time scales and solution compositions are no less physiologically relevant, but fall outside the range of applicability of the classical formalism. Here we show that the complete picture of an enzyme's mode of function is critically obscured by the limited scope of conventional kinetic analysis, even in the simplest case of a single active site without inhibition. This picture is now unveiled in a mathematically closed form that remains valid over the reaction time for all combinations of enzyme/substrate concentrations and rate constants. Algebraic simplicity is maintained in the new formalism when stationary reaction phases are considered. By achieving this century-old objective, the otherwise hidden role of the reversible binding step is revealed and atypical kinetic profiles are explained. Most singular kinetic behaviors are identified in a critical region of conditions that coincide with typical cell conditions. Because it is not covered by the Michaelis-Menten model, the critical region has been missed until now by low- and high-throughput screenings of new drugs. New possibilities are therefore raised for novel and once-promising inhibitors to therapeutically target enzymes.
authors: Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Portugal.
authors: Maria F
authors: http://orcid.org/0000-0002-6337-3459
authors: MF
authors: Pinto
authors: Laboratório de Engenharia de Processos, Ambiente, Biotecnologia e Energia (LEPABE), Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Portugal.
authors: Berta N
authors: BN
authors: Estevinho
authors: Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Portugal.
authors: Rosa
authors: R
authors: Crespo
authors: Laboratório de Engenharia de Processos, Ambiente, Biotecnologia e Energia (LEPABE), Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Portugal.
authors: Fernando A
authors: FA
authors: Rocha
authors: Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Portugal.
authors: Ana M
authors: AM
authors: Damas
authors: Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Portugal.|Laboratório de Engenharia de Processos, Ambiente, Biotecnologia e Energia (LEPABE), Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Portugal.
authors: Pedro M
authors: PM
authors: Martins
mesh_terms: D000465:Algorithms; D000818:Animals; D055162:Biocatalysis / Q000187:drug effects*; D002645:Chickens; D004798:Enzymes / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism; D005696:Galactosidases / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D009113:Muramidase / Q000378:metabolism
chemical_list: D004798:Enzymes; D029968:Escherichia coli Proteins; D005696:Galactosidases; C421864:hen egg lysozyme; D009113:Muramidase
keywords: Michaelis-Menten equation; enzyme inhibitors; enzyme kinetics; mathematical model; renewal theory