Nitric oxide dismutation

Keywords Superoxide Nitric oxide Manganese superoxide dismutase Manganese SOD mimetics (mimics) Peroxynitrite Nitric oxide dismutation Nitric oxide reduction. 

The relationship between EC-SOD expression and NO production in cells is of a great physiological and pathophysiological significance. In 1992, Oury et al. [35] demonstrated that EC-SOD increased oxygen toxicity in central nervous system (CNS) by the inhibition of superoxide-mediated inactivation of nitric oxide. This conclusion is obviously erroneous one because, as it is well known that the interaction of superoxide and nitric oxide results in the formation of a very toxic peroxynitrite. Indeed, the same authors recently showed that EC-SOD promoted nitric oxide vasodilation by dismuting superoxide [36]. On the other hand, it has been found that nitric oxide can downregulate the synthesis of EC-SOD by smooth muscle cells [37]. 

Nitric oxide is not in itself very reactive or particularly toxic. However, its interaction with other oxidants may yield products whose toxicity may result of significance. Such is the case of peroxynitrite (ONOO ) which is formed in a non-enzymatic reaction between NO and O2-. This reaction follows a 1 1 stoichiometry and it has a very fast reaction speed (6.7 X 10 mol/L s [40] which is 3 times higher than the capacity of O2 dismutation by SOD and around 1000 times greater than the reaction of NO with iron-sulfiir clusters [41 ]. 

However, these indirect effects of nitric oxide derived products are far more prevalent under pathological conditions such as inflammation, where the production of both NO and by the professional phagocytic cell NADPH oxidase enzyme, and induction of iNOS yields the potent cytotoxic species peroxynitrite. Whilst nitric oxide will react with metal centres (as discussed above) at a rate of 5x 10 M" s and the superoxide anion can be dismutated by SOD at a rate of 2.3x10 M s the combined reaction below (Eq. 9), proceeds at a rate faster than either of these individual reactions ... 

A superoxide free radical (Of) is produced from an enzyme called NADPH oxidase mostly in mitochondrion (Rios-Arrabal et al, 2013). It is less reactive than a hydroxyl radical (OH), but much more selective. Its lifetime is not longer than few seconds in biological systems, and it reacts with another superoxide molecule (self-dismutation reaction) to form a hydrogen peroxide. Superoxide also reacts with a nitric oxide to form a peroxynitrite, a very potent oxidant that belongs to reactive nitrogen species (RNS) (Juranek et al, 2013 Kalyanaraman, 2013 Miguel, 2010 Sahin Basak and Candan, 2013). 

The advantage of using the Micrococcaceae in fermented sausage production is a more reliable colour formation and colour stabilisation, together with enhancement of aroma. The cured colour is due to nitrosyl-myoglobin, a component obtained in the reaction of nitric oxide with myoglobin. The Micrococcaceae possess the necessary enzyme nitrate reductase that transforms nitrate into nitrite. In an acid environment, nitrite is converted into nitrous acid that is dismutated into nitric oxide. 

The study showed that ( )-a-bisabolol prevented the ethanol-induced increase of MDA, showing its antioxidant activity. The substance increased the SOD activity and the dismutation of superoxide anion and it prevented the reduction in CAT activity. (—)-ot-Bisabolol also reduced the influx of neutrophils in the gastric lesions. In agreement with the findings mentioned in the previous study, the pathway of nitric oxide is not related to the effect, because the substance did not significantly modify the nitrite levels. 

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