Mechanisms of ROS and RNS Signaling in Enzymatic Catalysis

Superoxide, hydrogen peroxide (H2O2), NO, and peroxynitrite (ONOO−) are major signaling species identied in numerous enzymatic processes. Two of them, O2·− and NO, are paramagnetic free radicals, whereas H2O2 and ONOO− are diamagnetic molecules. As a rule, it is difcult to study separately all these reactive species because two pairs (O2·− and H2O2) and (NO and ONOO−) are always formed together and are easily converted to each other. Of course, all of these are well-known facts, but they should be mentioned for the understanding of signaling functions of a particular ROS or RNS.