Antioxidative activity of nitrite in metmyoglobin induced lipid peroxidation

The antioxidative activity of nitrite in metmyoglobin (MMb)-initiated lipid peroxidation in linoleic acid emulsions was examined using oxygen consumption measurement. Nitrite decreased MMb-induced lipid peroxidation with increasing concentrations. The antioxidative effect of nitrite was independent of pH in the range 6.3-5.5, and 1% NaCl did not seem to influence the antioxidative activity of nitrite. Furthermore, nitrite reduced MMb denaturation during MMb-induced peroxidation of linoleic acid. Thermal analysis using differential scanning calorimetry showed that nitrite increased the denaturation temperature of MMb. However, direct complexation between nitrite and the iron center of MMb could not be confirmed using chromatographic methods and analysis of UV-visible spectra of mixtures of nitrite and MMb. The observed results can rather be explained by a weak reversible interaction between nitrite and MMb such as binding of nitrite at the entrance to the haem cavity protecting MMb against heat denaturation and protecting both MMb and the fatty acids against oxidative degradation.