Table 1.

Different members of the ROS family and their attributes

ROS	T1/2 (μs)	Subcellular origins	Mechanism of action	Reaction with DNA	Reaction with protein
Superoxide (O2•−)	1–4	Membranes, chloroplasts, and mitochondria	Reacts with redox-active proteins (e.g., Fe–S proteins)	None or extremely low	Via the Fe center
Hydroxyl radical (•OH)	<1	Membranes, chloroplasts, and mitochondria	Extremely reactive with all biomolecules	Very reactive	Very reactive
H2O2	1000	Membranes, chloroplasts, mitochondria, and peroxisome	Oxidizes proteins and forms •OH via O2•−	None or extremely low	Attacks Cys residue
Singlet oxygen (1O2)	1–4	Membranes, chloroplasts, and mitochondria	Oxidizes proteins, polyunsaturated fatty acids, and DNA	Very reactive	Attacks Trp, His, Tyr, Met, and Cys residues