Mechanism Of Deoxyribonucleic Acid And Its Bases Damage By Oxygen Species

Deoxyribonucleic acid (DNA) double helix is a long chain type polymers, formed the chromosome and gene, and stored the genetic imformation for survival and reproduction of organisms. Nucleotide is the basic composition unit of DNA, which consists of phosphoric acid, pentose and purine or pyrimidine base. DNA can be permanent damaged by variety physical and chemical factors, especially the light, radiation and photochemical, manifested as alter the structure of DNA, decomposition of pentose, transversion and looping of bases, leading to illness, aging and death of organism.Calf thymus DNA,·OH formed by ?-Fe2O3and bismuth oxybromide (BiOBr) with visible irradiation and O2-formed by ultraviolet irradiation were selected as research object, while the photochemical damage mechanism and diversity of DNA were especially focused. Typical bases (guanine, thymine and cytosine) in strands of DNA were selected as research object, O2-,·OH and hole formed by BiOBr and TiO2with ultraviolet irradiation, researched the photochemical damage mechanism of typical bases, combined the HMO methods to analyze the correlation between four nitrogenous bases and activity of oxidative damage, demonstrated the photochemical mechanism of DNA damage is of potential concern to bases damage, shed and open process. The main results are as follows:1. Calf thymus DNA were selected as research object and ?-Fe2O3as photochemical material to understand the mechanism of DNA damage by·OH under visible irradiation, calculated the energy parameters of four DNA bases by HMO methods to analyze the correlation between structure of bases and activity of oxidative damage. DNA damage process was measured by high-performance liquid chromatography (HPLC), especially the intermediate products, looping mode and attack sites of DNA damage were detected by LC-MS. The concentration of reactive oxygen species (ROS) and H2O2were tracked by fluorescence and spectrophotometry methods. The results indicated that ?-Fe2O3with visible irradiation can efficiently activates H2O2to generate·OH. The mechanism of oxidative DNA damage by photochemical is of potential concern to hydroxylation and looping of guanine-cytosine and adenine-thymine base pairs. Double bond of purine bases at N7-C8and pyrimidine bases at C5-C6were easier bonus, the vulnerable C8position of purine bases and C6of pyrimidine bases also were especially easy attacked by ROS. Among the four nitrogenous bases, thymine and guanine was most liable to oxidation by ROS.2.BiOBr were selected as photochemical material and calf thymus DNA as research object, O2-· and·OH formed by BiOBr under UV and Vis irradiation respectively, DNA damage process were measured by HPLC and agarose gel electrophoresis (AGE), the intermediate products, looping mode and attack sites of DNA damage were especially detected by LC-MS, the concentration of ROS and H2O2were tracked by ESR and spectrophotometry methods, to understand the essential difference on mechanism of oxidation of DNA damage by O2-· and·OH. The results indicated that the degree of DNA damage was serious by O2-· and·OH. The products of DNA damage by O2-· were guanine-cytosine base pairs and similar to the structure of8-oxo-7,8-dihydro-2-deoxyguanosine (8-oxodG), however the·OH can direct hydroxyle, shed and loop of guanine-cytosine base pairs.3. Based on the photochemical mechanism of oxidative DNA damage is of potential concern to decomposition of pentose and looping of bases. Guanine was selected as research object, BiOBr was used to analyze the mechanism details of guanine photochemical oxidation by O2-· under UV irradiation, further to demonstrate the photochemical mechanism of DNA damage. Guanine damage process was measured by HPLC and stability of BiOBr was analyzed by five photochemical sycle and ion chromatography (IC), especially the intermediate products, looping mode and attack sites of guanine damage were detected by LC-MS. The type of ROS was tracked by ESR method. The results indicated that BiOBr was a well stability photochemical material. Two oxidative guanine damage produces with molecular ion mass of m/z130and156, respectively, neither found8-oxodG with m/z168, however, the most plausible formation pathway of oxidised guanidinohydantoin (oxGH) with m/z156was through8-oxodG intermediate damage. The present work implicates that the commonly-used biomarker8-oxodG for DNA damage have application limitations.4. Pyrimidine bases (thymine and cytosine) in strands of DNA were selected as research object, TiO2was used to understand the essential difference on generation of·OH and hole in water or acetonitrile solution and mechanism of oxidative pyrimidine bases (thymine and cytosine) damage under UV irradiation, combined with antagonists of ROS (formic acid, isopropyl alcohol and methanol) to research the inhibition mechanism of pyrimidine bases damage. Pyrimidine bases (thymine and cytosine) damage process were measured by HPLC, especially the intermediate products, looping mode and attack sites of pyrimidine bases (thymine and cytosine) damage were detected by LC-MS. The type and trend of ROS was tracked by ESR method. Compared with the mixed solution, the degree of pyrimidine bases were serious in pure water and organic (acetonitrile) phase. It is noticed that not only DMPO-·OH but also DMPO-carbon-centered radical appeared gradually in UV/TiO2water solution when pyrimidine bases (thymine and cytosine) was presence, and DMPO-hole radical in organic (acetonitrile) phase. The inhibition or protection mechanism of antagonists is of potential concern to compete or capture the ROS process. Hole and·OH both can damage thymine and cytosine looping, among them the degree of thymine damage was most serious by·OH can direct heterogeneous thymine to uracil (U).