Oldreive C, Zhao K, Paganga G, Halliwell B, Rice-Evans C
International Antioxidant Research Centre at UMDS-Guy's Hospital, London SE1 9RT, and International Antioxidant Research Centre at King's College, Manresa Road, London SW3 6LX, U.K.
Chem Res Toxicol. 1998 Dec;11(12):1574-9. doi: 10.1021/tx980163p.
Exposure of tyrosine or DNA bases to acidic nitrite at low pH results in the nitration of tyrosine and the formation of base deamination products, respectively. At pH 1, hypoxanthine and xanthine are formed from the deamination of adenine and guanine, respectively, whereas under the same conditions, uracil is not detected. The yield of 3-nitrotyrosine derived from interaction of equimolar nitrite and tyrosine at pH 1 is approximately 50% of that obtained from equimolar peroxynitrite-tyrosine interactions at pH 7. 4. The ability of a range of plant phenolic constituents to prevent damage mediated by acidic nitrite was also examined in comparison with the activity of vitamin C. The epicatechin/gallate family of flavonols, constituents of green tea, red wine, etc., demonstrates the most extensive inhibitory properties against both tyrosine nitration and base deamination. The results also show that ascorbic acid is a poor inhibitor of nitration or deamination under acidic conditions such as those of the stomach. The ability of plant phenolics to scavenge reactive nitrogen species derived from acidic nitrite may contribute to the protective effects of tea polyphenols against gastric cancer.
在低pH值下，酪氨酸或DNA碱基暴露于酸性亚硝酸盐会分别导致酪氨酸硝化和碱基脱氨产物的形成。在pH 1时，腺嘌呤和鸟嘌呤脱氨分别形成次黄嘌呤和黄嘌呤，而在相同条件下未检测到尿嘧啶。在pH 1时，等摩尔亚硝酸盐与酪氨酸相互作用产生的3-硝基酪氨酸产量约为pH 7.4时等摩尔过氧亚硝酸盐与酪氨酸相互作用所得产量的50%。与维生素C的活性相比，还研究了一系列植物酚类成分预防酸性亚硝酸盐介导的损伤的能力。绿茶、红酒等中的黄酮醇表儿茶素/没食子酸家族对酪氨酸硝化和碱基脱氨均表现出最广泛的抑制特性。结果还表明，在胃部等酸性条件下，抗坏血酸对硝化或脱氨的抑制作用较弱。植物酚类清除酸性亚硝酸盐衍生的活性氮物种的能力可能有助于茶多酚对胃癌的保护作用。
