Santos C X, Anjos E I, Augusto O
Instituto de Química, Universidade de São Paulo, São Paulo, SP, Cx P. 26077, 05599-970, Brazil.
Arch Biochem Biophys. 1999 Dec 15;372(2):285-94. doi: 10.1006/abbi.1999.1491.
Uric acid has been considered to be an efficient scavenger of peroxynitrite but the reaction between urate and peroxynitrite has been only partially characterized. Also, previous studies have indicated that urate may increase peroxynitrite-mediated oxidation of low density lipoprotein (LDL). Here, we examined the reaction between urate and peroxynitrite by combining kinetic, oxygen consumption, spin trapping, and product identification studies; in parallel, we tested the effect of urate upon peroxynitrite-mediated lipid oxidation. Our results demonstrated that urate reacts with peroxynitrite with an apparent second order rate constant of 4.8 x 10(2) M(-1). s(-1) in a complex process, which is accompanied by oxygen consumption and formation of allantoin, alloxan, and urate-derived radicals. The main radical was identified as the aminocarbonyl radical by the electrospray mass spectra of its 5, 5-dimethyl-l-pyrroline N-oxide adduct. Mechanistic studies suggested that urate reacts with peroxynitrous acid and with the radicals generated from its decomposition to form products that can further react with peroxynitrite anion. These many reactions may explain the reported efficiency of urate in inhibiting some peroxynitrite-mediated processes. Production of the aminocarbonyl radical, however, may propagate oxidative reactions. We demonstrated that this radical is likely to be the species responsible for the effects of urate in amplifying peroxynitrite-mediated oxidation of liposomes and LDL, which was monitored by the formation of lipid peroxides and thiobarbituric acid-reactive substances. The aminocarbonyl radical was not detectable during urate attack by other oxidants and consequently it is unlikely to be responsible for all previously described prooxidant effects of uric acid.
尿酸被认为是过氧亚硝酸盐的有效清除剂，但尿酸盐与过氧亚硝酸盐之间的反应仅得到部分表征。此外，先前的研究表明尿酸盐可能会增加过氧亚硝酸盐介导的低密度脂蛋白（LDL）氧化。在此，我们通过结合动力学、耗氧、自旋捕获和产物鉴定研究来检测尿酸盐与过氧亚硝酸盐之间的反应；同时，我们测试了尿酸盐对过氧亚硝酸盐介导的脂质氧化的影响。我们的结果表明，尿酸盐与过氧亚硝酸盐反应，其表观二级速率常数为4.8×10² M⁻¹·s⁻¹，这是一个复杂的过程，伴随着耗氧以及尿囊素、尿囊酸和尿酸盐衍生自由基的形成。通过其5,5 - 二甲基 - 1 - 吡咯啉N - 氧化物加合物的电喷雾质谱，主要自由基被鉴定为氨基羰基自由基。机理研究表明，尿酸盐与过氧亚硝酸以及由其分解产生的自由基反应形成产物，这些产物可进一步与过氧亚硝酸盐阴离子反应。这些众多反应可能解释了所报道的尿酸盐在抑制某些过氧亚硝酸盐介导过程中的效率。然而，氨基羰基自由基的产生可能会促进氧化反应。我们证明该自由基可能是导致尿酸盐放大过氧亚硝酸盐介导的脂质体和LDL氧化作用的物质，这通过脂质过氧化物和硫代巴比妥酸反应性物质的形成来监测。在尿酸盐受到其他氧化剂攻击时未检测到氨基羰基自由基，因此它不太可能是先前描述的尿酸所有促氧化作用的原因。
