Nitrations of Tyrosine and Tryptophan by Peroxynitrite Treatment

生体内で生成するベルオキシナイトライトはタンパク質中のチロシン残基をニトロ化することが知られているが,このタンパク質中のニトロチロシンはヒトや動物の病変部位で見つかっている。そこで,タンパク質中の芳香族アミノ酸残基であるチロシンとトリプトファンのペルオキシナイトライトに対する反応性を調べる目的で,様々のpH条件下で遊離のチロシンとトリプトファンのニトロ化のされやすさを比較した。その結果,両アミノ酸のニトロ化はpH7.4の生理的条件下が最も起きやすく,3-ニトロチロシソより6-ニトロトリプトファンの方が生成しやすいことがわかった。
It is well known that tyrosine residues in proteins are the target of peroxynitrite to form nitrotyrosine residues. The tyrosine nitration in specific proteins in vivo has been detected in a number of human and animal models of disease. In this report, we studied the nitration of tyrosine and tryptophan with peroxynitrite with different pH conditions, and the reactions were compared. In acidic pH, two reaction products of tyrosin with peroxynitrite were detected, one of which was 3-nitrotyrosine, but in alkaline pH, many kinds of products were formed. In the case of tryptophan, many nitration and oxidation products which included 6-nitrotryptophan were detected in alkaline pH conditions. Although nitration of tyrosine and tryptophan by peroxynitrite were pH-dependent in quantity, relatively higher yield of 6-nitrotryptophan than that of 3-nitrotyrosine was obtained at a physiological condition of pH 7.4. These results suggest peroxynitrite formed in vivo will induce not only nitration of tyrosine residues in protein but also that of tryptophan residues.