title: Nonequilibrium linear behavior of biological systems. Existence of enzyme-mediated multidimensional inflection points.
abstract: The linear phenomenological equations of nonequilibrium thermodynamics are limited theoretically to near equilibrium although a number of biological systems have been shown to exhibit a "linear" relationship between steady-state flows and conjugate thermodynamic forces outside the range of equilibrium. We have found a multidimensional inflection point which can exist well outside the range of equilibrium around with enzyme-catalyzed reactions exhibit "linear" behavior between the logarithm of reactant concentrations and enzyme catalyzed flows. A set of sufficient conditions has been derived which can be applied to any enzyme mechanism to determine whether a multidimensional inflection point exists. The conditions do not appear overly restrictive and may be satisfied by a large variety of coupled enzyme reactions. It is thus possible that the linearity observed in some biological systems may be explained in terms of enzyme operating near this multidimensional point.
mesh_terms: D004798:Enzymes / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D013816:Thermodynamics
chemical_list: D004798:Enzymes