Cooperative interactions in photosensitized modification of DNA with oligonucleotide-derived binary reagents

Quantitative characteristics of thermodynamic and kinetic cooperativity ari sing 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 comple mentary 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 mo dified by the arylazide residue, which was activated owing to the contiguit y with the sensitizing perylene group in the tandem complex. Basing on the kinetic data, the constants of association of both derivatives of oligonucl eotides with the target were determined: K-x = 1.13 . 10(6) M-1, K-s = 1.49 . 10(4) M-1. It was determined that association of both oligonucleotides w ith the target proceeded with a positive cooperativity characterized by par ameter ct = 45. The kinetic cooperativity parameter beta was found to be ap proximately equal to 200; this characterized the acceleration of target mod ification in complex with the binary reagent versus that in the absence of sensitizer.