Signaling Functions of Free Radicals Superoxide &; Nitric Oxide under Physiological &; Pathological Conditions |
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Authors: | Igor B Afanas’ev |
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Institution: | (1) Vitamin Research Institute, Moscow, Russia |
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Abstract: | Superoxide and nitric oxide are ubiquitous physiological free radicals that are responsible for many pathological disorders.
Both radicals by themselves are relatively harmless but are the precursors of many toxic species such as peroxy and hydroxyl
radicals, hydrogen peroxide, and peroxynitrite. However, it has been shown now that both superoxide and nitric oxide are also
able to perform important signaling functions in physiological and pathophysiological processes. Wrongly named “superoxide,”
the radical anion of dioxygen is not a super-oxidant but the strong super-nucleophile, an efficient catalyst of heterogenic
nucleophilic reaction. Due to this, superoxide plays an important role in many enzymatic processes such as the phosphorylation
and activation of numerous protein kinases. On the other hand, superoxide inhibits the activation of phosphatases, the enzymes
catalyzed by dephosphorylation of protein kinases. We suggest that superoxide catalyzes these enzymatic processes as a result
of its nucleophilic properties. Another important physiological function of superoxide and nitric oxide is their competition
for the interaction with mitochondrial cytochrome c oxidase. Disturbance of superoxide/nitric oxide balance leads to the dysfunction of mitochondria and the enhancement of apoptosis
and oxidative stress, which are primary causes of various pathological disorders and aging. In conclusion, interplay between
superoxide and nitric oxide, one of major factors of aging development, is considered. |
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Keywords: | Superoxide Nitric oxide Protein kinases Aging |
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