POLYCYCLIC AROMATIC HYDROCARBON (PAH) ORTHO-QUINONE CONJUGATE CHEMISTRY - KINETICS OF THIOL ADDITION TO PAH ORTHO-QUINONES AND STRUCTURES OF THIOETHER ADDUCTS OF NAPHTHALENE-1,2-DIONE
POLYCYCLIC AROMATIC HYDROCARBON (PAH) ORTHO-QUINONE CONJUGATE CHEMISTRY - KINETICS OF THIOL ADDITION TO PAH ORTHO-QUINONES AND STRUCTURES OF THIOETHER ADDUCTS OF NAPHTHALENE-1,2-DIONE
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DOI：
10.1016/0009-2797(92)90077-x
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发表时间：
1992-09-28
影响因子：
5.1
通讯作者：
PENNING, TM
中科院分区：
文献类型：
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作者：
MURTY, VS;PENNING, TM
多环芳烃邻苯二酚是二氢二醇脱氢酶(EC 1.3.1.20)催化非K区反式二氢二醇依赖于NaDP+氧化的产物。由于这些多环芳烃邻苯二酚可以通过与细胞硫醇的非酶或酶偶联来解毒，因此用离子对反相高效液相色谱(RP-HPLC)研究了它们与2-巯基乙醇、半胱氨酸和谷胱甘肽(GSH)的反应活性。这些硫醇与1，2-萘-1，2-二酮(NPQ)在水中加成的二级速率常数范围为4.9×10(3)-1.1×10(4)min-1M-1，反应在10min内完成。当这些反应在接近生理pH(50 mM磷酸二氢钾缓冲液，pH 7.0)下进行时，速率常数增加了2个数量级。当取代苯并[a]芘-7，8-二酮(BPQ)时，反应的二级速率常数降低2-3个数量级，反应需要几个小时才能完成。反应活性的降低可以用BPQ中海湾区域的存在来解释。甲基化反应影响邻苯二酚与谷胱甘肽的反应活性，反应顺序如下：7，12-二甲基苯并[a]-3，4-二酮(7，12-DMBAQ)远大于12-甲基-BAQ，7-甲基-BAQ和BAQ远大于BPQ。其中，7，12-二甲基-BAQ与NPQ的反应基本相同。这表明湾区和周边区的甲基取代增强了与GSH的反应活性。以对苯二酚为模型化合物，合成了对苯二酚的N-乙酰基-L半胱氨酸、L-半胱氨酸和谷胱甘肽三种偶合物，并用[H-1]和[C-13]核磁共振对其结构进行了表征。获得了Michael类型1，4-加成产物的证据，其中生成的加合物可以以邻苯二酚或邻苯二酚的形式存在。相反，L-半胱氨酸通过S或N-基形成加合物，N-基得到紫色对亚氨基醌。没有证据表明有双-N-乙酰基-L-半胱氨基、双-谷胱甘肽加合物或酚偶联产物的形成。NPQ的硫醇结合物的毒性仍有待研究。
Polycyclic aromatic hydrocarbon (PAH) o-quinones are products of an NADP+ dependent oxidation of non-K-region trans-dihydrodiols catalyzed by dihydrodiol dehydrogenase (EC 1.3.1.20). Since these PAH o-quinones could be detoxified by non-enzymatic or enzymatic conjugation with cellular thiols, their reactivity with 2-mercaptoethanol, cysteine and glutathione (GSH) was examined by ion-pair reverse phase high pressure liquid chromatography (RP-HPLC). Second-order rate constants for the addition of these thiols to naphthalene-1,2-dione (NPQ) in water ranging from 4.9 x 10(3)-1.1 x 10(4) min-1 M-1 and the reactions were complete within 10 min. When these reactions were conducted at near physiological pH (50 mM potassium phosphate buffer pH 7.0), the rate constants increased by 2-orders of magnitude. When benzo[a]pyrene-7,8-dione (BPQ) was substituted in these reactions the second-order rate constants decreased by 2-3 orders of magnitude and the reactions took several hours to reach completion. The decrease in reactivity can be explained by the presence of the bay region in BPQ. Methylation influenced the reactivity of PAH o-quinones with GSH and the following order of reactivity was observed: 7,12-dimethyl-benz[a]anthracene-3,4-dione (7,12-DMBAQ) much greater than 12-methyl-BAQ, 7-methyl-BAQ and BAQ much greater than BPQ. Of these quinones 7,12-dimethyl-BAQ was almost equi-reactive with NPQ. This suggests that methyl substitution in the bay and peri regions enhances reactivity with GSH. Using NPQ as a model for other PAH o-quinones, N-acetyl-L-cysteine, L-cysteine and GSH conjugates of NPQ were synthesized and characterized by [H-1]- and [C-13]NMR. Evidence for Michael type 1,4-addition products was obtained in which the resultant adduct could exist as either a catechol or o-quinone. By contrast, L-cysteine was able to form adducts via S- or N-attack and N-attack gave a purple p-iminoquinone. There was no evidence for the formation of bis-N-acetyl-L-cysteinyl-, bis-glutathionyl adducts or phenolic coupled products. The toxicity of thiol conjugates of NPQ remains to be explored.