Antioxidant cytochrome c-like activity of para-MnTMPyP.

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/Mn redox couple. In CL-containing liposomes, MnTMPyP was reduced by superoxide ions and recycled by Fecytochrome c to the oxidized form. Similarly, isolated rat liver mitoplasts added to a sample of MnTMPyP promoted immediate porphyrin reoxidation by electron transfer to the respiratory chain. These results show that MnTMPyP can act as an additional pool of Fecytochrome c capable of transferring electrons that escape from the IV complex back into the respiratory chain. Unlike Fecytochrome c, MnTMPyP was not efficient for hydrogen peroxide clearance. Therefore, by reducing cytochrome c, MnTMPyP can indirectly contribute to hydrogen peroxide elimination.