We present evidence showing that a small fraction of electrophoretically homogeneous IgGs from the sera of healthy Wistar rats is bound with several different Me2+ ions and oxidizes 3,3'-diaminobenzidine through a peroxidase activity in the presence of H2O2 and through an oxidoreductase activity in the absence of H2O2. During purification on Protein A-Sepharose and gel filtration, the polyclonal IgGs partially lose the Me2+ ions. Therefore, in the absence of external metal ions, the specific peroxidase activity of IgGs from the sera of different rats varied in the range 1.6-26% and increased up to 13-198% after addition of Fe2+ or Cu2+ ions as compared with horseradish peroxidase (HRP, taken for 100%). The oxidoreductase activity of HRP is 24-fold lower than its peroxidase activity, while oxidoreductase and peroxidase activities of IgGs are comparable. Oxidoreductase activities of different IgGs in the absence of external metal ions varied from 22 to 800%, and in the presence of Fe2+ or Cu2+ ions, from 37 to 1100% in comparison with the HRP oxidoreductase activity (100%). Chromatography of the IgGs on Chelex-100 leads to the adsorption of a small IgG fraction bound with metal ions and to its separation to many different subfractions demonstrating various affinities to the chelating resin and increased levels of the specific oxidoreductase and peroxidase activities. Antioxidant enzymes such as superoxide dismutases, catalases, and glutathione peroxidases are known to represent critical defense mechanisms for preventing oxidative modifications of DNA, proteins, and lipids. Peroxidase and oxidoreductase activity of antibodies may play an important role in the protection of organisms from oxidative stress and toxic compounds.

Various catalytic antibodies or abzymes (Abzs) have been detected recently in the sera of patients and animals with many autoimmune diseases, where their presence is most probably associated with autoimmunization.

We have recently shown that intact IgGs from the sera of healthy Wistar rats oxidize 3,3'-diaminobenzidine (DAB) in the presence and in the absence of H(2)O(2) similar to horseradish peroxidase (HRP). Here we demonstrate for the first time that the peroxidase and oxidoreductase activities of IgGs can efficiently oxidize not only DAB but also o-phenylendiamine, phenol, p-dihydroquinone, alpha-naphthol, and NADH but, in contrast to HRP, cannot oxidize adrenalin. In contrast to IgGs, HRP cannot oxidize phenol, p-dihydroquinone, or alpha-naphthol in the absence of H(2)O(2). In contrast to plant and mammalian peroxidases, IgGs were more universal in their metal dependence. The specific wide repertoire of polyclonal peroxidase and oxidoreductase IgGs oxidizing various substances could play an important role in protecting the organism from oxidative stress and serve as an additional natural system destroying different toxic, carcinogenic, and mutagenic compounds.