Lindquist B E, Warshawsky D
University of Cincinnati Medical Center, Department of Environmental Health, Kettering Laboratory, OH 45267-0056.
Carcinogenesis. 1989 Dec;10(12):2187-95. doi: 10.1093/carcin/10.12.2187.
The N-heterocyclic aromatic pollutant, 7H-dibenzo[c,g]carbazole (DBC), is a potent carcinogen having both local and systemic effects. The overall objective of this research was to investigate the nature of the covalent binding of DBC with nucleic acids in vitro. DBC was shown to bind to polynucleotides, RNA and DNA in an in vitro rat or hamster microsomal enzyme assay, exhibiting a preferential binding to polyguanylic acid (poly[G]). Benzo[a]pyrene (BaP) binding to these same nucleic acids was determined simultaneously and was approximately 10-fold higher than DBC binding under identical experimental conditions. DBC-nucleic acid binding was shown to be dependent upon the presence of a microsomal activating system, the results being similar for rat or hamster liver microsomes. This microsome-dependent binding was unaffected by the addition of epoxide hydrase activity modifiers but was almost completely inhibited by alpha-naphthoflavone. The nature of DBC-nucleic acid binding was investigated using fluorescence spectroscopy. Benzo[c]carbazole and 5,5,6,6-tetrahydrodibenzo[c,g]carbazole were synthesized as representatives of the effect of disruption of the DBC pi-electron system on fluorescence excitation and emission. DBC-poly[G] adducts were isolated from binding assay mixtures and separated by HPLC. Results indicated that there are at least three different DBC-poly[G] adducts formed in vitro. The emission spectra of isolated adducts were similar in shape to that of DBC; however, the adduct spectra were shifted 5-10 nm toward longer wavelengths. This suggests that the bound DBC species have intact pi-electron systems. Results are consistent with binding through the nitrogen position as well as binding through the 1,2,3,4-ring of the molecule.
N-杂环芳香族污染物7H-二苯并[c,g]咔唑（DBC）是一种具有局部和全身效应的强效致癌物。本研究的总体目标是在体外研究DBC与核酸共价结合的性质。在体外大鼠或仓鼠微粒体酶试验中，DBC被证明可与多核苷酸、RNA和DNA结合，对聚鸟苷酸（poly[G]）表现出优先结合。同时测定了苯并[a]芘（BaP）与这些相同核酸的结合情况，在相同实验条件下，其结合量比DBC高约10倍。DBC与核酸的结合被证明依赖于微粒体激活系统的存在，大鼠或仓鼠肝微粒体的结果相似。这种依赖微粒体的结合不受环氧水解酶活性调节剂添加的影响，但几乎完全被α-萘黄酮抑制。使用荧光光谱法研究了DBC与核酸结合的性质。合成了苯并[c]咔唑和5,5,6,6-四氢二苯并[c,g]咔唑，作为DBC π电子系统破坏对荧光激发和发射影响的代表。从结合试验混合物中分离出DBC-poly[G]加合物，并通过高效液相色谱法进行分离。结果表明，体外至少形成了三种不同的DBC-poly[G]加合物。分离出的加合物的发射光谱形状与DBC相似；然而，加合物光谱向更长波长方向移动了5-10 nm。这表明结合的DBC物种具有完整的π电子系统。结果与通过氮位置以及通过分子的1,2,3,4-环结合是一致的。
