Photocleavage of Plasmid pBR322 DNA by Some Anionic Porphyrins

Abstract

The water-soluble porphyrins meso-tetrakis[4-(carboxymethyleneoxy)phenyl]porphyrin ( 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 induced SSBs in DNA as a function of irradiation time as well as porphyrin concentration. Under similar conditions (10 μM or more), H 2 T3CPP showed more SSBs in DNA than the porphyrins H 2 T 4CPP and H 2 T 3,4 BCPP . The DNA cleavage was more in D 2 O -based buffer than in H 2 O buffer. In addition, this DNA cleavage was inhibited by the presence of sodium azide and lipoic acid, which are potent quenchers of singlet oxygen (1 O 2). These observations suggest the involvement of 1 O 2 in photocleavage of DNA. Further, the DNA cleavage, to a limited extent, was also inhibited by tert-butanol and mannitol, both quenchers of hydroxyl radical (· OH ), suggesting the involvement of · OH in photocleavage of DNA. Thus both 1 O 2 and · OH are involved in photocleavage of plasmid DNA by these porphyrins.