Superoxide anion radicals biosynthesis

N-Acetyl-l-cysteine (NAC), another significant precursor of the GSH biosynthesis, has broadly been used as effective antioxidant in a form of nutritional supplement (Soloveva M. E et al 2007, Thibodeau P. A., et al 2001). At low concentrations, it is a powerful protector of a-l-antiproteinase against the enzyme inactivation by HOCl. NAC reacts with HO radicals and slowly with H O however, no reaction of this endobiotics with superoxide anion radical was detected [88]. 

Dopamine- -hydroxylase is another copper enzyme that plays a major function in the biosynthesis of norepinephrine (40). A protective catalyst, superoxide dismutase, has been described to catalyze the dismu-tation of the superoxide anion free radical (41). Other enzymes known to contain copper are the laccases, the phenol oxidases, and the ascorbic acid oxidases (12). 

Despite the orderly process of enzyme biosynthesis and the denaturation and degradation of older enzymes, there are problems of stability of proteins in solution. There is continual endogenous generation of peroxides, ammonia, hydrogen ions, carbon monoxide, superoxide, singlet oxygen, and hydroxyl radicals. Oxygen, as well as cations, anions, and trace metals are present in all cellular fluids. These various substances may inhibit or destabilize various enzymes. 

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