Hierarchical Organization of Modularity in Metabolic Networks
E. Ravasz,1
A. L. Somera,2
D. A. Mongru,2
Z. N. Oltvai,2*
A.-L. Barabási1*
Spatially or chemically isolated functional modules
composed of several cellular components and carrying discrete functions are considered fundamental building blocks of cellular organization, but their presence in highly integrated biochemical networks lacks quantitative support. Here, we show that the metabolic networks of 43 distinct organisms are organized into many small, highly connected
topologic modules that combine in a hierarchical manner into larger,
less cohesive units, with their number and degree of clustering
following a power law. Within Escherichia coli, the
uncovered hierarchical modularity closely overlaps with known metabolic
functions. The identified network architecture may be generic to
system-level cellular organization.
1 Department of Physics, University of Notre
Dame, Notre Dame, IN 46556, USA.
2 Department of
Pathology, Northwestern University, Chicago, IL 60611, USA.
*
To whom correspondence should be addressed. E-mail:
zno008{at}northwestern.edu (Z.N.O.) and alb{at}nd.edu (A.-L.B.)
