Kirsch Michael, Lehnig Manfred
Institut für Physiologische Chemie, Universitätsklinikum Essen, Hufelandstrasse 55, D-45122 Essen, Germany.
Org Biomol Chem. 2005 Jun 7;3(11):2085-90. doi: 10.1039/b502915e. Epub 2005 Apr 29.
The novel reaction of N-acetyl-N-nitrosotryptophan (NANT) with hydrogen peroxide to yield peroxynitrite is demonstrated. Quantum chemical calculations performed at CBS-QB3 level of theory predicted that the reaction of N-nitrosoindole with both H(2)O(2) and its corresponding anion is thermodynamically feasible. At pH 13, the formation of peroxynitrite from the bimolecular reaction of NANT with H(2)O(2) is unequivocally demonstrated by (15)N NMR spectrometry. In order to prove the intermediacy of peroxynitrite from the NANT-H(2)O(2) system at neutral (7.4) and acidic pH (4.5), the characteristic pattern of CIDNP (chemically induced dynamic nuclear polarization) signals were recorded, i.e. enhanced absorption in the (15)N NMR signal of nitrate and emission in the (15)N NMR signal of nitrite. Most interestingly, the NANT-H(2)O(2) system nitrated N-acetyltyrosine at pH 4 via recombination of freely diffusing nitrogen dioxide and tyrosyl radicals, but nitration was negligible at pH 7.4. Since the combination between NANT and H(2)O(2) is slow, endogenous N-nitrosotryptophan residues cannot act as a "carrier" for peroxynitrite.
本文展示了N-乙酰基-N-亚硝基色氨酸（NANT）与过氧化氢反应生成过氧亚硝酸根的新反应。在CBS-QB3理论水平上进行的量子化学计算预测，N-亚硝基吲哚与H₂O₂及其相应阴离子的反应在热力学上是可行的。在pH 13时，通过¹⁵N NMR光谱明确证明了NANT与H₂O₂的双分子反应生成过氧亚硝酸根。为了证明在中性（7.4）和酸性pH（4.5）条件下NANT-H₂O₂体系中过氧亚硝酸根的中间体性质，记录了化学诱导动态核极化（CIDNP）信号的特征模式，即硝酸盐的¹⁵N NMR信号增强吸收，亚硝酸盐的¹⁵N NMR信号发射。最有趣的是，NANT-H₂O₂体系在pH 4时通过自由扩散的二氧化氮和酪氨酸自由基的重组使N-乙酰基酪氨酸硝化，但在pH 7.4时硝化作用可忽略不计。由于NANT与H₂O₂的结合缓慢，内源性N-亚硝基色氨酸残基不能作为过氧亚硝酸根的“载体”。
