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

Abstract

meso-Tetrakis[4-(carboxymethyleneoxy)phenyl]porphyrin (H 2T4CPP) 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 D 2O buffer of sodium phosphate (pD=7.4) than H 2O buffer of sodium phosphate (pH=7.4). In addition this photocleavage of plasmid DNA was inhiited in the presence of sodium azide, lipoic acid, tert-butanol or mannitol suggesting the involvement of 1O 2 and OH in the photocleavage of plasmid DNA. The photocleavage was observed to be more efficient in the presence of H 2T4CPP than in the presence of H 2CPP [ meso-tetrakis(4-carboxyphenyl)porphyrin]. Our spectral studies using UV-visible, fluorescence and circular dichroism techniques suggest that H 2T4CPP binds to DNA while H 2CPP does not. Thus, the difference in photocleavage may be caused by the nonbinding of H 2CPP and by the binding of H 2T4CPP to calf thymus (CT) DNA.