Reactivities of chemical substances with human protooncogene in application to screening of carcinogenicity

用~（13）P标记的人c-ha-ras-1原癌基因DNA片段，用DNA测序技术研究了金属离子存在下致癌物与DNA的反应<32>。(1)苯的代谢产物1，2，4-苯三酚即使不经碱处理也能引起DNA的强烈损伤。1，2，4-苯三酚诱导的碱不稳定位点是鸟嘌呤和邻近胸腺嘧啶的碱基残基。过氧化氢酶、超氧化物歧化酶和蛋氨酸可完全抑制DNA损伤，甲酸钠不能抑制DNA损伤，Cu（I）特异性螯合剂可抑制DNA损伤，而Cu（II）可加速DNA损伤。结果表明，Cu（Ⅱ）对DNA的损伤作用不是由羟基自由基引起的，而是由1，2，4-苯三酚在Cu（Ⅱ）存在下自氧化产生的未完全降解的活性物种引起的。同样，2，5-二羟基联苯，邻苯基苯酚代谢产物，诱导位点特异性DNA损伤的铜（II）的presene。(2)致癌物质是公认的。 ...更多信息 c铬（VI）、次氮基三乙酸铁（III）和钴（II）与过氧化氢反应，导致产生包括羟基自由基和单线态氧的活性物质，其引起DNA损伤。致癌性镍（II）与DNA结合，随后与过氧化氢反应形成活性物质，诱导DNA损伤。活性物种似乎是镍-氧络合物，而不是单线态氧或自由羟基自由基。(3)在存在C 0 ^&lt;2+&gt;、Cu^&lt;2+&gt;和Mn^&lt;2+&gt;的情况下，亚硫酸盐可引起DNA损伤。对亚硫酸盐依赖性DNA损伤的诱导作用顺序为Co^&lt;2+&gt;&gt;Cu^&lt;2+&gt;Mn^&lt;2+&gt;&gt;Fe^&lt;3+&gt;，与对亚硫酸盐自氧化起始耗氧速率的加速作用顺序一致。用亚硫酸盐和Co^&lt;2+&gt;孵育DNA，导致鸟嘌呤尤其是位于鸟嘌呤5'端的位置上的主要裂解。亚硫酸盐加Cu^&lt;2+&gt;诱导的DNA裂解模式与亚硫酸盐加Co^&lt;2+&gt;诱导的DNA裂解模式不同。过二硫酸盐（S_2O^2-）的光解作用可以产生SO^-自由基，它产生的DNA裂解模式与亚硫酸盐加Co^&lt;2+&gt;诱导的DNA裂解模式相似。结果表明，亚硫酸盐在Co^&lt;2+&gt;存在下迅速自氧化产生SO^-_2自由基，引起DNA的位点特异性损伤。少

The reactivities of carcinogen with DNA in the presence of metal ions were investigated by a DNA sequencing technique using ^<32>P-labeled DNA fragments obtained from human c-ha-ras-1 protooncogene.(1) 1,2,4-Benzenetriol, a benzene metabolite, caused strong DNA damage even without alkali treatment. Alkali-labile sites induced by 1,2,4-benzenetriol were base residues of guanine and adjacent thymine. Catalase, SOD and methional inhibited the DNA damage completely, but sodium formate did not inhibit it. The DNA damage was inhibited by the addition of Cu(I)-specific chelating agent, and was accelerated by the addition of Cu(II). The results suggest that the DNA damage was caused by unidenitified active species which was produced by the autoxidation of 1,2,4-benzenetriol in the presence of Cu(II), rather than by hydroxyl radicals. Similarly, 2,5-dihydroxybiphenyl, an 0-phenylphenol metabolite, induced site-specific DNA damage in the presene of copper(II).(2) It is calrified that carcinogeni … More c chromium(VI),iron(III)nitrilotriacetate, and cobalt(II)react with hydrogen peroxide leading to the production of active species including hydroxyl radical and singlet oxygen, which cause DNA damage. Carcinogenic nickel(II) binds to DNA and subsequently reacts with hydrogen peroxide to form active species, which induces DNA damage. The active species seems to be a nickel-oxygen complex rather than singlet oxygen or free hydroxyl radical.(3) Sulfite caused DNA damage in the presence of C0^<2+>,Cu^<2+> and Mn^<2+>. The order of inducing effect on sulfite-dependent DNA damage( Co^<2+>>>Cu^<2+>>Mn^<2+>>Fe^<3+>) was consistent with that of accelerating effect on the initial oxygen consumption rate of sulfite autoxidation. Incubation of DNA with sulfite plus Co^<2+> led to the predominant cleavage at the positions of guanine especially located 5' to guanine. Sulfite plus Cu^<2+> gave a DNA cleavage pattern different from that induced by sulfite plus Co^<2+>. The photolysis of peroxydisulfate (S_2o^2-_), which is known to produce SO^-_ radicals, gave a DNA cleavage pattern simiar to that induced by sulfite plus Co^<2+>. The results suggest that sulfite is rapidly autoxidized in the presence of Co^<2+> to produce SO^-_ radicals causing site-specific DNA damage. Less