the system behavior is far more dependent on the network structure than the exact parameters used. The analysis presented here lends some support to that finding, since only a few reactions could have different effect on the system if the parameters are wrong. A further scan of initial conditions for metabolites found that varying initial concentrations over 2 orders of magnitude had no affect on the steady state achieved (Table \[tab:tableOfSS\]), indicating that the steady state found in these simulations is unique.

Receptor Properties {#receptor-properties .unnumbered}
-------------------

It is known that the iron sensing by the transferrin receptors is responsive over a wide range of intercellular iron concentrations [@Lin2007Iron]. The present model reproduces this well (Figure \[fig:TfRResponse\]A, $1\times$ turnover line). Becker [*et al.*]{} argued that a linear response of a receptor to its signal over a wide range could be achieved through a combination of: high receptor abundance, increased expression when required, recycling to the surface of internalised receptors and high receptor turnover [@Becker2010Covering]. This was illustrated with the behaviour of the erythropoietin (EPO) receptor [@Becker2010Covering]. Since the present model contains essentially the same type of reactions that can lead to such a behaviour, simulations were carried out to investigate 