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. Author manuscript; available in PMC: 2015 Jul 1.
Published in final edited form as: Int J Biochem Cell Biol. 2014 Mar 20;0:113–123. doi: 10.1016/j.biocel.2014.03.006

Figure 1.

Figure 1

Classic definition of oxidative stress. Cellular redox homeostasis is maintained as a balance between oxidizing and reducing equivalents (Eq). Because thiol moieties can undergo reversible oxidation/reduction that provide a mechanism to facilitate, protein function, protein-protein interactions, protein-DNA interactions and protein trafficking, many Eq couples of interest contain thiol resides including GSH/GSSG, Cys/CySS and Trxred/Trxox, but other non-thiol based redox Eq can include NADH/NAD and NADPH/NADP among others. Regulation is a consequence of cellular ROS tone, balance of reductases and oxidases and metabolic equilibrium. During periods of ROS overproduction, reduced Eq can be overwhelmed allowing oxidized Eq to predominate. In turn, increasing concentrations of ROS can augment interaction with various macromolecules, such as DNA, proteins and lipids, causing often irreversible damage. If unchecked, accumulation of damage will lead to cellular apoptosis.