RESUMO
Manganese porphyrins are well-known protectors against the deleterious effects of pro-oxidant species such as superoxide ions and hydrogen peroxide. The present study investigated the antioxidant cytochrome c-like activities of Mn(III)TMPyP [meso-tetrakis (4-N-methyl pyridinium) porphyrin] against superoxide ion and hydrogen peroxide that remained unexplored for this porphyrin. The association of TMPyP with a model of the inner mitochondrial membrane, cardiolipin (CL)-containing liposomes, shifted +30 mV vs. NHE (normal hydrogen electrode) redox potential of the Mn(II)/Mn(III) redox couple. In CL-containing liposomes, Mn(III)TMPyP was reduced by superoxide ions and recycled by Fe(III)cytochrome c to the oxidized form. Similarly, isolated rat liver mitoplasts added to a sample of Mn(II)TMPyP promoted immediate porphyrin reoxidation by electron transfer to the respiratory chain. These results show that Mn(III)TMPyP can act as an additional pool of Fe(III)cytochrome c capable of transferring electrons that escape from the IV complex back into the respiratory chain. Unlike Fe(II)cytochrome c, Mn(II)TMPyP was not efficient for hydrogen peroxide clearance. Therefore, by reducing cytochrome c, Mn(II)TMPyP can indirectly contribute to hydrogen peroxide elimination.