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

1.用同步辐射产生的单色光子在远紫外光(300-200 nm)、真空-紫外光(190-50 nm)、软X射线(约0.5 nm)和~(60)Coγ射线等宽波长范围内对胸腺嘧啶核苷(DTpdT)进行了固态(真空)辐照。用高效液相色谱法对dTpdT的光产物进行分析，在220 nm波长处测定吸光度，用高效液相色谱峰面积测定其含量。从~(60)Coγ射线的测量结果是否可以看作是真空-紫外光测量结果的叠加的角度，研究了光学近似计算dTpdT中光生产物的可行性。环丁烷型胸腺嘧啶二聚体和(6-4)光生产物的产生量在260 nm处最高，向短波长方向下降，在140 nm以下变得不可检测。这两种双嘧啶类光产物仅在远紫外区有效产生。主要由210nm光和0.001 nm光(^&lt；…)产生更多的是胸腺嘧啶(T)、3‘-TMP和5’-TMP，它们是通过破坏脱氧核糖部分而产生的。这些光解产物之间的比例几乎与波长无关。在2.153 keV(磷原子的共振吸收峰处)X射线诱导的磷的K壳层激发和随后的俄歇效应没有特殊的影响。这些结果表明，当能量大于6 eV(波长低于200 nm)时，通过激发、超激发或电离外层或内层电子，dTpdT分子的脱氧核糖部分被选择性地破坏。因此，这些结果与光生产物诱导的光学近似的可行性不冲突。经2.153 keV X射线175mR辐照的寡核苷酸，其主要产物为T，5‘-TMP和核苷酸数目从2到9的寡核苷酸。5’-TMP和每个寡核苷酸光产物的数目大致相同，它们的总数大约相当于T的数目，说明所有的脱氧核糖都被同等破坏，一次破坏产生一个T和两个核苷酸类型的产物(单核苷酸和寡核苷酸)。较少

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