Proteins reactions with hypochlorite

Proteins, due to the complexity of their chemical structures, undergo oxidative modifications in subsequent stages which depend both on the presence of oxidation-susceptible groups and on steric availability of these groups for oxidant attacks (S25). Some oxidative structural modifications produced in proteins are common in various oxidants. Some modifications, such as chlorinated and nitrated protein derivatives produced in reactions with hypochlorite, peroxynitrite, and nitric dioxide, are specific for the oxidants employed. Certain oxidative protein modifications, such as interchain or intrachain disulfide bond formation or thiolation, are reversible and may be reduced back to the protein native form when oxidative stress is over (Dl). Other changes, such as sulfone formation, chlorination, and nitration, are irreversible and effect protein denaturation and promote its subsequent degradation. 

Isotope labeling experiments have shown chlorite to be the sole source of the oxygen atoms in the O2 product.30 EPR and UV-Vis studies also suggest that Cld forms a compound I-like intermediate upon reaction with CIO2. However, the hypochlorite (CIO ) by-product is believed to not diffuse freely into solution, but instead remains protein bound for further reaction with the ferryl to afford 02. The mechanism illustrated in Figure 3.8 has been put forth for this unique heme enzyme. 

Metal chelation may enhance or inhibit the Fenton reaction, depending on the metal and the chelator in question. Chelation of iron (II) by EDTA enhances the formation of hydroxyl radical, while deferoxamine, another chelator, reduces its formation. This is significant because peptides or proteins can chelate metals in the body, thus influencing the resulting degree of damage. The formation of hydroxyl radicals by nickel (II) and cobalt (II) is enhanced by this type of chelation. In addition to the Fenton and Haber-Weiss reactions, metals can also catalyze the formation of the hydroxyl radical via reaction with hypochlorite (HOCl), which is prodnced by neutrophils. ... 

Satisfactory alternatives to the hydrolytic procedures have been sought for many years. Methods have been tried to produce colored derivatives by exploiting the reactivity of the indole nucleus in the intact protein (135, 353). Sodium hypochlorite, ferric chloride, cupric sulfate, bromine, and sodium nitrite, usually in acid solution, have been found to produce color with tryptophan-containing proteins. Later workers have formed other colored derivatives by reaction with tryptophan-specific reagents, while still others have used the characte-... 

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