Study of Optical Approximation to Photoproduct Formation in Oligonucleotides by Action Spectra (50 - 300 nm).

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1. Thymidylyl- (3'->5') -thymidine (dTpdT) was irradiated in solid state (in vacuum) with monochromatic photons from synchrotron radiation over the wide range of wavelength : far-UV (300 - 200 nm), vacuum-UV (190 - 50 nm), soft X-rays (about 0.5 nm) and ^<60>Co gamma-rays. Photoproducts of dTpdT were analyzed by high performance liquid chromatography (HPLC), detected by absorbance at 220 nm and determined the quantities by the peak areas of HPLC chromatogram. The feasibility of optical approximation to photoproduct formation in dTpdT is studied from the viewpoint whether the results by ^<60>Co gamma-rays can be regarded as the superposition of the results by vacuum-UV.The production of cyclobutane type thymine dimers and (6-4) photoproduct were highest at 260 nm, decreased toward shorter wavelengths and became undetectable below 140 nm. These two dipyrimidine photoproducts were produced efficiently in far-UV region only.Main photoproducts induced by photons between 210 and 0.001 nm (^< … More 60>Co gamma-ray) were thymine (T), 3'-TMP and 5'-TMP, which were produced through destruction of deoxyribose moiety. The ratios among amounts of these photolysis products were almost independent on wavelength. The K-shell excitation of phosphorus induced by 2.153 keV (at resonance absorption peak of phosphorus atom) X-rays and following Auger effects had no special effect. These results indicate that deoxyribose moiety of dTpdT molecule is selectively destroyed when energies above 6 eV (wavelength below 200 nm) are absorbed through excitation, superexcitation or ionization of outer or inner shell electrons. Hence, these results do not conflict with the feasibility of the optical approximation for photoproduct induction by ^<60>Co gamma-rays.2. Main products of oligonucleotide, (pdT)_<10>, irradiated by 175 MR of 2.153 keV X-ray were T, 5'-TMP and oligonucleotides with nucleotide number from 2 to 9. The 5'-TMP and each oligonucleotide photoproduct were produced approximately same number and their total number equaled to about the number of T, indicating that all deoxyribose were equally destroyed and one destruction produced one T and two nucleotide type products (mono and oligo). Less