Sign-sensitivity of metabolic networks: which structures determine the sign of the responses

TL;DR

This paper investigates how the structure of metabolic networks determines the sign of their responses to perturbations, using a purely stoichiometric, non-quantitative approach to identify key subnetworks influencing response signs.

Contribution

It introduces a structural method based solely on network stoichiometry to analyze response signs in metabolic systems, independent of reaction kinetics.

Findings

Identifies subnetworks linked to kernel vectors that determine response signs.

Shows that response sign patterns depend on network structure, not reaction rates.

Provides a framework to predict response directions without detailed kinetic data.

Abstract

Perturbations are ubiquitous in metabolism. A central tool to understand and control their influence on metabolic networks is sensitivity analysis, which investigates how the network responds to external perturbations. We follow here a structural approach: the analysis is based on the network stoichiometry only and it does not require any quantitative knowledge of the reaction rates. We consider perturbations of reaction rates and metabolite concentrations, at equilibrium, and we investigate the responses in the network. For general metabolic systems, this paper focuses on the sign of the responses, i.e. whether a response is positive, negative or whether its sign depends on the parameters of the system. In particular, we identify and describe the subnetworks that are the main players in the sign description. These subnetworks are associated to certain kernel vectors of the stoichiometric matrix and are thus independent from the chosen kinetics.