  We show how active transport of ions can be interpreted as an entropy
facilitated process. In this interpretation, the pore geometry through which
substrates are transported can give rise to a driving force. This gives a
direct link between the geometry and the changes in Gibbs energy required.
Quantifying the size of this effect for several proteins we find that the
entropic contribution from the pore geometry is significant and we discuss how
the effect can be used to interpret variations in the affinity at the binding
site.
