Scale-rich metabolic networks: background and introduction
  Recent progress has clarified many features of the global architecture of biological metabolic networks, which have highly organized and optimized tolerances and tradeoffs (HOT) for functional requirements of flexibility, efficiency, robustness, and evolvability, with constraints on conservation of energy, redox, and many small moieties. One consequence of this architecture is a highly structured modularity that is self-dissimilar and scale-rich, with extremes in low and high variability, including power laws, in both metabolite and reaction degree distributions. This paper illustrates these features using the well-understood stoichiometry of metabolic networks in bacteria, and a simple model of an abstract metabolism. 
Reiko Tanaka and John Doyle