I. Metal-ion interactions and transmembrane permeability of peroxynitrite. II. DNA binding and cleavage mechanisms of metal chelate-appended porphyrins

I. Peroxynitrite (ONOO{dollar}sp-{dollar}) is formed by a rapid reaction between nitric oxide and superoxide and is considered to be a significant oxidant in vivo. Two important determinants of peroxynitrite toxicity in vivo are described: (i) The interactions of ONOO{dollar}sp-{dollar} with metal ions and metal-ion chelates and (ii) the permeability of ONOO{dollar}sp-{dollar} in model phospholipid membrane systems.; The reaction of peroxynitrite with a water-soluble manganese porphyrin (MnTMPyP) resulted in the formation of reactive oxomanganese species capable of accelerating DNA oxidation and phenolic nitration. Different oxomanganese species were involved in these reactions: While DNA oxidation was mediated by oxoMn(V) species, phenolic nitration was due to oxoMn(IV) and NO{dollar}sb2sp.{dollar}.; Reporter manganese porphyrin molecules were deployed in the interior compartment of phospholipid vesicles (MnTMPyP) and in distinct positions in the lipid bilayer (MnChP, MnTMP, MnTCAmP). Peroxynitrite readily oxidized all these porphyrins to form observable oxoMn(IV) species, indicating ONOO{dollar}sp-{dollar} accessibility to these regions in vesicles. The permeability coefficient of ONOO{dollar}sp-{dollar} was found to be similar to that of water. Thus, ONOO{dollar}sp-{dollar} can be expected to freely travel through and across ion-impermeable phospholipid membranes.; II. The DNA binding and cleavage mechanisms of dicationic porphyrins cis-DPAM and trans-DPAM are described. Both porphyrins are equipped with two dipicolylamine (DPA) metal-chelating appendages, each capable of independently cleaving DNA. The porphyrins accessed different DNA-binding modes (outside binding (cis-DPAM) and intercalation (trans-DPAM)). However, their DNA cleavage patterns and product yields were similar, indicating that cleavage due to the DPA ligands was not affected by the porphyrin binding modes. The product yields from the cis-DPAM and trans-DPAM were more than twice as high as yields from mono-DPAM, a porphyrin with a single DPA ligand. This supports earlier observations that DNA cleavage due to cis-DPAM and trans-DPAM is non-random and can lead to lethal double-strand breaks.