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

meso-Tetrakis [4-(carboxymethylenzoxy)phenyl]porphyrin (H(2)T4CPP) 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 O-1(2) and OH in the photocleavage of plasmid DNA. The photocleavage was observed to be more efficient in the presence of H2CPP than in the presence of H(2)T4CPP [meso-tetrakis(4-carboxy-phenyl) porphyrin]. Our spectral studies using UV-visible, fluorescence and circular dichroism techniques suggest that H(2)T4CPP binds to DNA while H(2)T4CPP does not, Thus, the difference in photocleavage may be caused by the nonbinding of H2CPP and by the binding of H(2)T4CPP to calf thymus (CT) DNA. (C) 1997 Elsevier Science S.A.