Cooperative Interactions in Photosensitized Modification of DNA with Oligonucleotide-derived Binary Reagents

Quantitative characteristics of thermodynamic and kinetic cooperativity arising in the process of photomodification of a single-stranded DNA fragment with binary systems of oligonucleotide conjugates forming an active site on the target were studied. Oligonucleotides of the binary system were complementary to adjacent segments of the DNA target, and contained arylazide (X) and perylene (S) residues covalently attached to their terminal phosphates. Upon irradiation at the perylene absorption wavelength, the target was modified by the arylazide residue, which was activated owing to the contiguity with the sensitizing perylene group in the tandem complex. Basing on the kinetic data, the constants of association of both derivatives of oligonucleotides with the target were determined: K _x = 1.13 · 10⁶ M^–1, K _s = 1.49 · 10⁴ M^–1. It was determined that association of both oligonucleotides with the target proceeded with a positive cooperativity characterized by parameter = 45. The kinetic cooperativity parameter was found to be approximately equal to 200; this characterized the acceleration of target modification in complex with the binary reagent versus that in the absence of sensitizer.