  Characterizing the capabilities, criticalities and response to perturbations
of genome-scale metabolic networks is a basic problem with important
applications. A key question concerns the identification of the potentially
most harmful knockouts. The integration of combinatorial methods with sampling
techniques to explore the space of viable flux states may provide crucial
insights on this issue. We assess the replaceability of every metabolic
conversion in the human red blood cell by enumerating the alternative paths
from substrate to product, obtaining a complete map of the potential damage of
single enzymopathies. Sampling the space of optimal flux states in the healthy
and in the mutated cell reveals both correlations and complementarity between
topologic and dynamical aspects.
