Switching in mass action networks based on linear inequalities

TL;DR

This paper develops linear inequality-based conditions to analytically identify switching behavior in mass action networks, focusing on saddle-node bifurcations, which broadens the analysis beyond traditional bistability approaches.

Contribution

It introduces a novel analytical method using linear inequalities to detect saddle-node bifurcations in mass action networks, applicable under certain conditions.

Findings

Conditions for saddle-node bifurcations are derived analytically.

Applicable to general mass action networks with conservation relations.

Method provides a complementary approach to numerical bifurcation analysis.

Abstract

Many biochemical processes can successfully be described by dynamical systems allowing some form of switching when, depending on their initial conditions, solutions of the dynamical system end up in different regions of state space (associated with different biochemical functions). Switching is often realized by a bistable system (i.e. a dynamical system allowing two stable steady state solutions) and, in the majority of cases, bistability is established numerically. In our point of view this approach is too restrictive, as, one the one hand, due to predominant parameter uncertainty numerical methods are generally difficult to apply to realistic models originating in Systems Biology. And on the other hand switching already arises with the occurrence of a saddle type steady state (characterized by a Jacobian where exactly one Eigenvalue is positive and the remaining eigenvalues have negative real part). Consequently we derive conditions based on linear inequalities that allow the analytic computation of states and parameters where the Jacobian derived from a mass action network has a defective zero eigenvalue so that -- under certain genericity conditions -- a saddle-node bifurcation occurs. Our conditions are applicable to general mass action networks involving at least one conservation relation, however, they are only sufficient (as infeasibility of linear inequalities does not exclude defective zero eigenvalues).