In this project, we aim at applying electron paramagnetic resonance (EPR) spectroscopy to probe structure-function relationships in biological systems and attempt to develop a new mode of application. This year, in collaboration with Dr. Makoto Chikira, Special Volunteer, we studied by EPR the binding behavior of various metalloporphyrins, metal complexes of amino acids, and metal complexes of bleomycin on DNA fiber which is held oriented in EPR magnetic field. Some of these metal complexes have photosensitive character and others can activate molecular oxygen. One objective of this project is to determine how these complexes bind to DNA, i.e., the relationship between, e.g. the porphyrin structure and the base-pair sequence specificity of binding and the geometry of porphyrins on DNA. Specific example of results obtained are: 1) Cu(4TMpyP) --- tetramethylpyridin deritive---intercalates in DNA double helix, while Cu(4TMpyP)-imidazole complex and Cu(2TMpyP) bind to the groove of DNA double helix with the g11 axis, respectively, parallel and perpendicular to the groove, 2) EPR signals corresponding to both intercalated and groove-bound Co(4TMpyP) were resolved, and computer simulations of line shapes are now underway, 3) High spin Fe(4TMpyP) binds to the groove of DNA with the orientation similar to that of Cu(2TMpyP). Low spin bisimidazole adduct of Fe(4TMpyP) binds to the DNA with the porphyrin plane being parallel g(x) axis being almost perpendicular to the DNA fiber axis. In the case of oxygenated Co(II)bleomycin complex, the oxygen-oxygen bond is restricted to a plane perpendicular to the fiber axis.
