The Michaelis-Menten-Henri (MMH) mechanism is one of the paradigm reaction mechanisms in biology and chemistry. In its simplest form, it involves a substrate that reacts (reversibly) with an enzyme, forming a complex which is transformed (irreversibly) into a product and the enzyme. Given these basic kinetics, a dimension reduction has traditionally been achieved in two steps, by using conservation relations to reduce the number of species and by exploiting the inherent fast–slow structure of the resulting equations. In the present article, we investigate how the dynamics change if the species are additionally allowed to diffuse. We study the two extreme regimes of large diffusivities and of small diffusivities, as well as an intermediate regime in which the time scale of diffusion is comparable to that of the fast reaction kinetics. We show that reduction is possible in each of these regimes, with the nature of the reduction being regime dependent. Our analysis relies on the classical method of matched asymptotic expansions to derive approximations for the solutions that are uniformly valid in space and time.

Singular perturbations (msc 35B25), Attractors (msc 35B41), Inertial manifolds (msc 35B42), Reaction-diffusion equations (msc 35K57)
Southwest Texas State University
Electronic Journal of Differential Equations
Computational Dynamics

Zagaris, A, Kalachev, L.V, Kaper, H.G, Kaper, T.J, & Popovic, N. (2007). Reduction for Michaelis-Menten-Henri kinetics in the presence of diffusion. Electronic Journal of Differential Equations, Con16, 155–184.