[Hydrogen peroxide as a signal molecule]

This review deals with numerous literature data on the action of small redox-active H2O2 biomolecule on the cellular activity. Evidence is provided on H2O2 sources in the cell, intracellular antioxidants and scavengers, and on the dependence of cellular response (cell damage or activation) on H2O2 concentration. Stimulation of cells by nontoxic doses of H2O2 and possible activation mechanisms are also discussed. The number of examples is given demonstrating H2O2 playing the role of a second messenger for the variety of agents that stimulate the cells.