Structure and Catalysis of Fe(III) and Cu(II) Microperoxidase-11 Interacting with the Positively Charged Interfaces of Lipids

Reactivity of inorganic sulfide species towards a pentacoordinated heme model system

The reactivity of inorganic sulfide towards ferric bis(N-acetyl)- microperoxidase 11 in sodium dodecyl sulfate has been explored by means of visible absorption and resonance Raman spectroscopies. The reaction has been previously studied in buffered solutions at neutral pH and in the presence of excess sulfide, revealing the formation of a moderately stable hexacoordinated low spin ferric sulfide complex that yields the ferrous form in the hour's timescale. In the surfactant solution, instead, the ferrous form is rapidly formed. The spectroscopic characterization of the heme structure in the surfactant milieu revealed the stabilization of a major ferric mono-histidyl high spin heme, which may be ascribed to out of plane distortions prompting the detachment of the axially ligated water molecule, thus leading to a differential reactivity. The ferric bis(N-acetyl)- microperoxidase 11 in sodium dodecyl sulfate provides a model for pentacoordinated heme platforms with an imidazole-based ligand.

Antioxidant cytochrome c-like activity of para-Mn(III)TMPyP

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.