  We show that spectral fluctuation of interaction matrices of yeast a core
protein interaction network and a metabolic network follows the description of
the Gaussian orthogonal ensemble (GOE) of random matrix theory (RMT).
Furthermore, we demonstrate that while the global biological networks evaluated
belong to GOE, removal of interactions between constituents transitions the
networks to systems of isolated modules described by the Poisson statistics of
RMT. Our results indicate that although biological networks are very different
from other complex systems at the molecular level, they display the same
statistical properties at large scale. The transition point provides a new
objective approach for the identification of functional modules.
