The binding of water-soluble meso-tetra-(4N-oxyethylpyridyl) porphyrin (H2TOEtPyP4) and its manganese (III) derivative (MnTOEtPyP4) with calf thymus DNA have been quantitatively studied using UV/Vis spectrophotometry, Circular Dichroism (CD), thermal melting curves and viscometry. The results show, that porphyrins interact with DNA via one binding mode at low relative concentrations (r) and two binding modes at high values of r. The binding constant (Kb) and stoichiometry (n) were determined from binding isotherms for both porphyrin-DNA complexes. The thermal melting analysis indicates that the double-helical structure of DNA molecules is stabilizing in presence of studied porphyrins. At certain concentrations of porphyrin, two-stage melting curves were observed, which indicates the existence of two different binding modes. Obtained results show that MnTOEtPyP4 associates with DNA duplex via outside binding mode.Communicated by Ramaswamy H. Sarma.
Keywords: viscosity; DNA; binding parameters; circular dichroism; melting curves; porphyrins.