Fig. 4.

ROS specific signaling microdomains. (A) Superoxide׳s sphere of influence. Upon illumination KillerRed (KR) generates superoxide (O₂^•−). The concentration of O₂^•− can be decreased by spontaneous dismutation or SOD activity, such that the local levels of O₂^•− available to modify/signal are affected. Areas residing close to the site of O₂^•− generation (2) may see a higher local concentration of areas than those further away (3). Since O₂^•− is a charged molecule, membrane permeability is limited and sites separated by a membrane (1) may not be affected. (B) Hydrogen peroxide׳s sphere of influence. O₂^•− can be rapidly converted to hydrogen peroxide (H₂O₂). The mitochondrial matrix lacks catalase and combined with the ability to cross membranes, H₂O₂ concentrations may be able to diffuse to affect a greater area and have a larger sphere of influence such that all areas may be affected.