Photocleavage of plasmid pBR322 DNA by some anionic porphyrins

The;water-soluble porphyrins meso-tetrakis[4-(carboxymethyleneoxy)phenyl]po rphyrin (H(2)T4CPP), meso-tetrakis[3-(carboxymethyleneoxy)phenyl]porphyrin (H(2)T3CPP) and meso-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl]porphyrin (H(2)T3,4BCPP) cleave plasmid pBR322 DNA to single-strand breaks (SSBs) in the presence of molecular oxygen and visible light. These porphyrins induce d SSBs in DNA as a function of irradiation time as well as porphyrin concen tration. Under similar conditions (10 mu M or more), H2T3CPP showed more SS Bs in DNA than the porphyrins H(2)T4CPP and H(2)T3,4BCPP. The DNA cleavage was more in D2O-based buffer than in H2O buffer. in addition, this DNA clea vage was inhibited by the presence of sodium azide and lipoic acid, which a re potent quenchers of singlet oxygen (O-1(2)). These observations suggest the involvement of O-1(2) in photocleavage of DNA. Further, the DNA cleavag e, to a limited extent, was also inhibited by tert-butanol and mannitol, bo th quenchers of hydroxyl radical ((OH)-O-.), suggesting the involvement of (OH)-O-. in photocleavage of DNA. Thus both O-1(2) and (OH)-O-. are involve d in photocleavage of plasmid DNA by these porphyrins. (C) 1998 John Wiley & Sons, Ltd.