Sheng D, Joshi D K, Gold M H
Department of Biochemistry and Molecular Biology, Oregon Graduate Institute of Science and Technology, Portland, Oregon 97291-1000, USA.
Arch Biochem Biophys. 1998 Apr 1;352(1):121-9. doi: 10.1006/abbi.1997.0570.
Lignin peroxidase (LiP), from Phanerochaete chrysosporium, in the presence of H2O2 and tetranitromethane (TNM), oxidizes veratryl (3,4-dimethoxybenzyl) alcohol (VA) (I) to veratraldehyde (IV), 4,5-dimethoxy-2-nitrobenzyl alcohol (V), and 3,4-dimethoxy-nitrobenzene (VI). The formation of these products is explained by a mechanism involving the one-electron oxidation of VA by LiP to produce the corresponding cation radical, which loses a proton to generate the benzylic radical. The latter reduces TNM to generate the trinitromethane anion (VIII) and the nitrogen dioxide radical (.NO2). .NO2 couples with the VA cation radical, and the subsequent loss of a proton leads to V. Alternatively, the attack of .NO2 at C-1 of the VA cation radical, followed by aromatization and loss of formaldehyde (VII), yields VI. Isotopic labeling experiments confirm that V is generated by the reaction of .NO2 with the VA cation radical, rather than with the benzylic radical. The nitration of two other LiP substrates, 1,4-dimethoxybenzene (II) and tyrosine (III), also was examined. Product analysis of reactions conducted in the presence of H2O2 with these substrates indicated less nitrated product was formed from 1,4-dimethoxybenzene and no nitrated product was formed from tyrosine. However, significant amounts of nitrated products were formed from 1,4-dimethoxybenzene and tyrosine when glucose and glucose oxidase were used as an H2O2 source. These results suggest that a reductant, either the veratryl alcohol benzylic radical or superoxide, is required in the reaction to reduce TNM to generate .NO2. These results provide further evidence for the formation of the VA cation radical and the first chemical evidence for the formation of the VA benzylic radical in LiP-catalyzed reactions.
来自黄孢原毛平革菌的木质素过氧化物酶（LiP），在过氧化氢（H₂O₂）和四硝基甲烷（TNM）存在的情况下，将藜芦醇（3,4 - 二甲氧基苄醇，VA）（I）氧化为藜芦醛（IV）、4,5 - 二甲氧基 - 2 - 硝基苄醇（V）和3,4 - 二甲氧基硝基苯（VI）。这些产物的形成可通过一种机制来解释，该机制涉及LiP对VA进行单电子氧化以产生相应的阳离子自由基，该阳离子自由基失去一个质子生成苄基自由基。后者将TNM还原以生成三硝基甲烷阴离子（VIII）和二氧化氮自由基（·NO₂）。·NO₂与VA阳离子自由基结合，随后失去一个质子生成V。另外，·NO₂对VA阳离子自由基的C - 1位进行攻击，随后发生芳构化并失去甲醛（VII），生成VI。同位素标记实验证实V是由·NO₂与VA阳离子自由基反应生成的，而不是与苄基自由基反应生成的。还研究了另外两种LiP底物1,4 - 二甲氧基苯（II）和酪氨酸（III）的硝化反应。在H₂O₂存在下对这些底物进行反应的产物分析表明，1,4 - 二甲氧基苯生成的硝化产物较少，而酪氨酸未生成硝化产物。然而，当使用葡萄糖和葡萄糖氧化酶作为H₂O₂来源时，1,4 - 二甲氧基苯和酪氨酸生成了大量的硝化产物。这些结果表明，反应中需要一种还原剂，要么是藜芦醇苄基自由基，要么是超氧化物，来将TNM还原以生成·NO₂。这些结果为VA阳离子自由基的形成提供了进一步的证据，并为LiP催化反应中VA苄基自由基的形成提供了首个化学证据。
