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ACTION SPECTRA FOR THE PHOTOLYSIS OF 5‐IODODEOXYURIDINE IN DNA AND RELATED MODEL SYSTEMS: EVIDENCE FOR SHORT‐RANGE ENERGY TRANSFER *
Author(s) -
Rahn R. O.,
Sellin H. G.
Publication year - 1982
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1982.tb02594.x
Subject(s) - polynucleotide , chemistry , dna , irradiation , quantum yield , excited state , analytical chemistry (journal) , photochemistry , atomic physics , biochemistry , chromatography , physics , quantum mechanics , nuclear physics , fluorescence
— A variety of polynucleotides containing 5‐iodouracil residues were irradiated in aqueous solution with wavelengths between 240 and 313 nm. From the rate of deiodination the photochemical cross sections (a B ) were determined as a function of the irradiation wavelength (A). The expression was used to relate the observed values of B to the intrinsic quantum yield, φ INT , and to the absorption cross sections, and for the iodinated and noniodinated residues, respectively. φ INT is the probability an excited iodouracil residue will deiodinate, while the parameter b is a measure of the number of noniodinated bases which contribute their excitation energy to the deiodination process. For IdUrd and poly(5‐iodouridylic acid), the average values of φ INT calculated from the experimental B values were 0.0202 and 0.0188, respectively, for irradiation in air. In native, denatured, and depurinated DNA in which IdUrd was substituted for 10% of the Thd, the average φ INT values were 0.0069, 0.0088, and 0.0153, respectively, indicating an enhancement in φ INT upon decreasing the order of the polynucleotide. In contrast, the average values of b bor the same set of compounds were found to be 4 , 2 and 0.4, respectively, indicating a decrease in b with decreasing polynucleotide order, i.e. a loss of base stacking decreases the extent of energy transfer. A value of b = 4 for native DNA is assumed to mean that the extent of energy transfer in native DNA is limited to four base donors per iodouracil residue serving as an energy trap.