DNA cleavage specificity of a group of cationic metalloporphyrins

The ability of a group of water-soluble metalloporphyrins to cleave DNA has been investigated. Incubation of Mn3+, Fe3+, or Co3+ complexes of meso-tetrakis(N-methyl-4-pyridiniumyl)porphine (H2T4MPyP) with DNA in the presence of ascorbate, superoxide ion, or iodosobenzene results in DNA breakage. Comparisons between the rates of porphyrin autodestruction with the rates of strand scission of covalently closed circular PM2 DNA indicate that the porphyrins remain intact during the cleavage process. Analysis of the porphyrin-mediated strand scissions on a 139-base-pair restriction fragment of pBR322 DNA using gel electrophoresis/autoradiography/microdensitometry reveals that the minimum porphyrin cleavage site is (A X T)3. The cleavage pattern within a given site was found to be asymmetric, indicating that porphyrin binding and the strand scission process are highly directional in nature. In addition to an analysis of the mechanism of porphyrin-mediated strand breakage in terms of the DNA cleavage mechanism of methidium-propyl-iron-EDTA and Fe-bleomycin, the potential of the cationic metalloporphyrins as footprinting probes and as new "reporter ligands" for DNA is presented and discussed.