  Experiments show that the movement of eukaryotic cells is regulated by a
process of phase separation of two competing enzymes on the cell membrane, that
effectively amplifies shallow external gradients of chemical attractant.
Notably, the cell is able to self-tune the final enzyme concentrations to an
equilibrium state of phase coexistence, for a wide range of the average
attractant concentration. We propose a simple lattice model in which, together
with a short-range attraction between enzymes, a long-range repulsion naturally
arises from physical considerations, that easily explains such observed
behavior.
