BioMetals 15: 357–365, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 357 Oxidative cleavage of DNA by homo- and heteronuclear Cu(II)-Mn(II) complexes of an oxime-type ligand Nagihan Saglam 1 , Ahmet Colak 1 , Kerim Serbest 1 , Sabriye Dülger 2 , Saadettin Güner 1,∗ , Serdar Karaböcek 1 & Ali Osman Beldüz 2 Departments of Chemistry 1 and Biology 2 , Karadeniz Technical University, 61080 Trabzon, Turkey; ∗ Author for correspondence (Tel: +(90)-462-377 2598; Fax: +(90)-462-325 3195: E-mail: sguner@ktu.edu.tr) Received 4 October 2001; Accepted 30 October 2001 Key words: chemical nuclease, copper, manganese, nucleolytic activity, oxime Abstract Novel homodinuclear Cu(II) (K1), heterodinuclear Cu(II)-Mn(II) (K2) and homotrinuclear Cu(II) (K3) complexes with a novel oxime-type ligand have been prepared and their nucleolytic activities on pCYTEXP were established by neutral agarose gel electrophoresis. The analyses of the cleavage products obtained electrophoretically indicate that although the examined complexes induces very similar conformational changes on supercoiled DNA by con- verting supercoiled form to nicked form than linear form in a sequential manner as the complex concentration or reaction period is increased, K3 is less effective than the two others. The oxime complexes were nucleolytically active at physiological pH values but the activities of K1 or K2 were diminished by increasing the pH of the reaction mixture. In contrast, K3 makes dominantly single strand nicking by producing nicked circles on DNA at almost all the applied pH values. Metal complex induced DNA cleavage was also tested for inhibition by various radical scavengers as superoxide dismutase (SOD), azide, thiourea and potassium iodide. The antioxidants inhibited the nucleolytic acitivities of the oxime complexes but SOD afforded no protection indicating that the nucleolytic mechanism involves of copper and/or manganese complex-mediated reactive oxygen species such as hydroxyl radicals being responsible for the oxidative DNA cleavage. Introduction In the recent years, the interaction of transition metal complexes with nucleic acids has gained much more attention (Barton 1986; Sigman & Chen 1990; Pa- pavassiliou 1995). These interactions are of great importance for the understanding of the requirements for designing new chemotherapeutic agents and de- veloping tools or probes for the study of nucleic acid structure. Of these, the hydrolytic cleavage of nucleic acids is of fundamental chemical and biochemical sig- nificance. However, it is well known that nucleic acids are generally not reactive upon hydrolysis in the ab- sence of an appropriate nucleolytic enzyme under mild conditions. In the last years, designing an effective chemical nuclease has been the focus of investiga- tion of metal-mediated nucleic acid hydrolysis since these redox active compounds cleave the phosphodi- ester backbone of DNA molecules under physiological pH and temperature (Sigman et al. 1979; Pope & Sigman 1984). Nucleolytic activities of several copper complexes with synthetic or natural ligands have been stud- ied extensively. The first synthetic complex possess- ing nucleic acid cleavage activity was the bis(1,10- phenanthroline)-copper(II) (Pope & Sigman 1984; Travers 1993). Several other compounds such as salen- (Gravert & Griffin 1993; Sato et al. 1994; Man- dal et al. 1996; Routier et al. 1996), porphyrin- (Groves & Farrell 1989), semicarbazone- (Reddy et al., 2000a, b), pyrrole- (Borah et al. 1998; Asad et al. 1999), thioether-(Dülger et al. 2000; Athar et al. 2001), and polyamine-type ligands (McLachlan et al. 1996) which were complexed with copper ions were also shown to have DNA-relaxation activities.