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Free Radicals, Types, Sources and Damaging Reactions

Submitted by Dr. Tamer Fouad, M.D.

Types of Free Radicals in the body (continued)

Singlet oxygen:

It is a nonradical (does not have an unpaired electron) reactive oxygen species often associated with oxygen free radicals that has strong oxidising activity. Singlet oxygen (1O2) is an electronically excited and mutagenic form of oxygen. It is generated by input of energy, example radiation, but can also be generated enzymatically by the action of peroxidases or lipoxigenases or by the reaction of hydrogen peroxide with hypochlorite or peroxynitrite (Di Mascio et al. 1994, Di Mascio et al. 1996), thermo-decomposition of dioxetanes (Briviba et al. 1996), or during the respiratory burst of phagocytes (Steinbeck et al. 1993). They are also generated in biological systems in a number of pigment reactions including chlorophylls, retinal and flavins when they are illuminated in the presence of oxygen.

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