Prof. Tomasz Lipniacki,
Instytut Podstawowych Problemow Techniki

Transitions between steady states of a multistable stochastic system in the perfectly mixed chemical
reactor are possible only due to stochastic switching. In realistic cellular conditions, where diffusion is limited, transitions between steady states can also follow from the propagation of travelling waves. Here we study the interplay between the two modes of transition for a prototype bistable system of kinase-phosphatase interactions on the plasma membrane. Within microscopic kinetic Monte Carlo simulations on the hexagonal lattice we observed that for finite diffusion the behaviour of the spatially extended system differs qualitatively from the behaviour of the same system in the wellmixed regime. Even when a small isolated subcompartment remains mostly inactive, the chemical travelling wave may propagate leading to the activation of a larger compartment. The activating wave can be induced after a small subdomain is activated as a result of a stochastic fluctuation. Such spontaneous onset of activity is radically more probable in subdomains characterized by slower diffusion. Our results show that a local immobilisation of substrates can lead to the global activation of membrane proteins by the mechanism which involves stochastic fluctuations followed by the propagation of a semi-deterministic travelling wave.