A model for switch-like phenomena in biological systems.

We present a model for the activity of protein clusters based on a simultaneous desorption of an activator (agonist, substrate molecule, etc.) and an inactivator (antagonist, inhibitor, etc.) caused by the collision or interaction between two effector molecules (e.g. receptors, enzymes). This model gives rise to switch-like dose-response curves, which are difficult to explain by ordinary co-operativity. It fits with recent experimental results obtained on single cells. Some other interesting aspects of the model are also pointed out. The model is similar to the model used to explain steep 'dose-response curves' in heterogeneous catalysis, caused by the reaction between two different molecules or atoms on the surface of the catalyst.