we added a new footnote, to explain our standing on this issue: Reference 36: In this work, concentrations outside the vesicle are set as system parameters. However, we make no commitment to the type of environment the vesicle is embedded in or how these concentrations are maintained. Our purpose is simply to show that bistability can exist in the model for certain sets of outside concentrations. Exploration of the model in explicit environments is deferred to future work.
Note 4 presents a very important issue: why the inner chemical environment is different from the external one, if the running chemical reactions are the same? The presence of particular features of the vesicle interior or of entrapped catalysts seem a too easy and ad hoc hypothesis. A useful reference proposing an explanation of this symmetry breaking (without requiring different conditions in internal and external environments) could be “R. Serra, M. Villani Mechanism for the formation of density gradients through semipermeable membranes Physical Review E 87, 2013”.