FIGURE 3.

Dismutation of superoxide (O2^–) by superoxide dismutase (A) or manganese (B). SOD reacts with O₂^– and generates H₂O₂ and O₂ that are less reactive (Melo et al., 2011). Studying the catalytic activity of manganese in different in vitro systems (in pyrophosphate or orthophosphate-buffered media) showed that in both situations, Mn²⁺ is oxidized by O₂^–, which forms Mn³⁺ and H₂O₂ and then the formed Mn³⁺ is re-reduced to Mn²⁺, and O₂ is produced. In the presence of pyrophosphate, O₂^– acts as both oxidizing and reducing agent; in the presence of orthophosphate or some other buffered media, another reductant such as NAD(P)H or H₂O₂ is required for the scavenging activity of manganese. The above-mentioned mechanisms potentially occur in the bacterial cell. However, the reaction rate and the reaction course are determined by the ligands that are available and can associate with manganese (Archibald and Fridovich, 1981).