— importantly, these physiological data were not used in constructing the model. This validation provides a sense of confidence that the model is indeed appropriate for understanding liver iron regulation and for predicting the response to various environmental perturbations.

Results {#results .unnumbered}
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Our model was constructed based on many published data on individual molecular interactions (see Methods section), and is available in Systems Biology Markup Language (SBML) and COPASI formats in supplementary data, as well as from BioModels (http://identifiers.org/biomodels.db/MODEL1302260000) [@LeNovere2006BioModels]. Figure \[bigDiagram\] depicts a process diagram of the model, using the Systems Biology Graphical Notation (SBGN) standard [@Novere2009Systems], where all the considered interactions are shown. It is important to highlight that while results described below are largely in agreement with observations, the model was not forced to replicate them. The extent of agreement between model and physiological data provides confidence that the model is accurate enough to carry out “what-if” type of experiments that can provide quantitative explanation of iron regulation in the liver.

Steady State {#steady-state .unnumbered}
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Initial validation of the model was performed by assessing the ability to recreate experimentally-observed steady-state concentrations of metabolites and rates of reactions. Simulations were run to steady state using the 