Photocleavage of plasmid DNA by the prophyrin meso-tetrakis[4-(carboxymethyleneoxy)phenyl]porphyrin.

meso-Tetrakis[4-(carboxymethyleneoxy)phenyl]porphyrin (H2T4CPP) cleaves pBR322 plasmid DNA to single strand breaks in the presence of molecular oxygen and visible light. The above photocleavage was much more efficient in D2O buffer of sodium phosphate (pD = 7.4) than H2O buffer of sodium phosphate (pH = 7.4). In addition this photocleavage of plasmid DNA was inhibited in the presence of sodium azide, lipoic acid, tert-butanol or mannitol suggesting the involvement of 1O2 and.OH in the photocleavage of plasmid DNA. The photocleavage was observed to be more efficient in the presence of H2T4CPP than in the presence of H2CPP [meso-tetrakis (4-carboxy-phenyl)porphyrin]. Our spectral studies using UV-visible, fluorescence and circular dichroism techniques suggest that H2T4CPP binds to DNA while H2CPP does not. Thus, the difference in photocleavage may be caused by the nonbinding of H2CPP and by the binding of H2T4CPP to calf thymus (CT) DNA.