title: Sensitivity analysis of metabolic cascades catalyzed by bifunctional enzymes.
abstract: Covalent modification/demodification cycles are common in metabolism. When the modification and demodification steps are carried out by two independent enzymes, the degree of modification can be ultrasensitive to the total concentration of either catalyst. We recently showed that the degree of modification of a target molecule cannot exhibit ultrasensitivity to the free concentrations of effectors that decide whether a bifunctional enzyme acts as modifier or demodifier. However, here we can now demonstrate that the degree of modification of a target molecule can display ultrasensitivity to the total, rather than free, concentrations of such effectors. Our results clarify some general aspects of ultrasensitive responses to effectors, including competitive inhibitors, in mono-cyclic cascades.
authors.affiliation: Centre de Química Teórica, and Departament de Química Física, Facultat de Química, Universitat de Barcelona, Catalonia, Spain. fortega@pcb.ub.es
authors.forename: Fernando
authors.initials: F
authors.lastname: Ortega
authors.forename: Måns
authors.initials: M
authors.lastname: Ehrenberg
authors.forename: Luis
authors.initials: L
authors.lastname: Acerenza
authors.forename: Hans V
authors.initials: HV
authors.lastname: Westerhoff
authors.forename: Francesc
authors.initials: F
authors.lastname: Mas
authors.forename: Marta
authors.initials: M
authors.lastname: Cascante
mesh_terms: D002384:Catalysis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes