  In living cells, biochemical reactions are catalyzed by specific enzymes and
connect to one another by sharing substrates and products, forming complex
networks. In our previous studies, we established a framework determining the
responses to enzyme perturbations only from network topology, and then proved a
theorem, called the law of localization, explaining response patterns in terms
of network topology. In this paper, we generalize these results to reaction
networks with conserved concentrations, which allows us to study any reaction
systems. We also propose novel network characteristics quantifying robustness.
We compare E. coli metabolic network with randomly rewired networks, and find
that the robustness of the E. coli network is significantly higher than that of
the random networks.
