Shear viscosity of two-state enzyme solutions

TL;DR

This paper models the shear viscosity of enzyme solutions considering enzyme conformational states and substrate interactions, linking viscosity to enzyme dynamics and diffusion properties.

Contribution

It introduces a two-state enzyme model to derive viscosity expressions based on enzyme conformational dynamics and substrate affinity.

Findings

Viscosity depends on substrate concentration and enzyme state.

Fast and slow enzymes show distinct viscosity behaviors.

Viscosity relates to tracer particle diffusion in enzyme solutions.

Abstract

We discuss the shear viscosity of a Newtonian solution of catalytic enzymes and substrate molecules. The enzyme is modeled as a two-state dimer consisting of two spherical domains connected with an elastic spring. The enzymatic conformational dynamics is induced by the substrate binding and such a process is represented by an additional elastic spring. Employing the Boltzmann distribution weighted by the waiting times of enzymatic species in each catalytic cycle, we obtain the shear viscosity of dilute enzyme solutions as a function of substrate concentration and its physical properties. The substrate affinity distinguishes between fast and slow enzymes, and the corresponding viscosity expressions are obtained. Furthermore, we connect the obtained viscosity with the diffusion coefficient of a tracer particle in enzyme solutions.