Redox Signaling - Exogenous ROS

Exogenous ROS

Exogenous ROS can be produced from pollutants, tobacco, smoke, drugs, xenobiotics, or radiation.

Ionizing radiation can generate damaging intermediates through the interaction with water, a process termed radiolysis. Since water comprises 55-60% of the human body, the probability of radiolysis is quite high under the presence of ionizing radiation. In the process, water loses an electron and become highly reactive. Then through a three-step chain reaction, water is sequentially converted to hydroxyl radical (-OH), hydrogen peroxide (H₂O₂), superoxide radical (O₂-) and ultimately oxygen (O₂). The hydroxyl radical is extremely reactive that immediately removes electrons from any molecule in its path, turning that molecule into a free radical and so propagating a chain reaction. But hydrogen peroxide is actually more damaging to DNA than hydroxyl radical since the lower reactivity of hydrogen peroxide provides enough time for the molecule to travel into the nucleus of the cell, subsequently wreaking havoc on macromolecules such as DNA.