Fontana Mario, Amendola Donatella, Orsini Emanuela, Boffi Alberto, Pecci Laura
Department of Biochemical Sciences A. Rossi Fanelli, Institute of Molecular Biology and Pathology of CNR, University of Rome La Sapienza, P.le Aldo Moro 5, I-00185 Rome, Italy.
Biochem J. 2005 Jul 1;389(Pt 1):233-40. doi: 10.1042/BJ20041696.
Peroxynitrite mediates the oxidation of the sulphinic group of both HTAU (hypotaurine) and CSA (cysteine sulphinic acid), producing the respective sulphonates, TAU (taurine) and CA (cysteic acid). The reaction is associated with extensive oxygen uptake, suggesting that HTAU and CSA are oxidized by the one-electron transfer mechanism to sulphonyl radicals, which may initiate an oxygen-dependent radical chain reaction with the sulphonates as final products. Besides the one-electron mechanism, HTAU and CSA can be oxidized by the two-electron pathway, leading directly to sulphonate formation without oxygen consumption. The apparent second-order rate constants for the direct reaction of peroxynitrite with HTAU and CSA at pH 7.4 and 25 degrees C are 77.4+/-5 and 76.4+/-9 M(-1).s(-1) respectively. For both sulphinates, the apparent second-order rate constants increase sharply with decrease in pH, and the sigmoidal curves obtained are consistent with peroxynitrous acid as the species responsible for sulphinate oxidation. The kinetic data, together with changes in oxygen uptake, sulphinate depletion, sulphonate production, and product distribution of nitrite and nitrate, suggest that oxidation of sulphinates by peroxynitrite may take place by the two reaction pathways whose relative importance depends on reagent concentrations and pH value. In the presence of bicarbonate, the direct reaction of sulphinates with peroxynitrite is inhibited and the oxidative reaction probably involves only the radicals NO2 and CO3-, generated by decomposition of the peroxynitrite-CO2 adduct.
过氧亚硝酸盐介导次牛磺酸（HTAU）和半胱氨酸亚磺酸（CSA）的亚磺酰基氧化，生成相应的磺酸盐，即牛磺酸（TAU）和磺基丙氨酸（CA）。该反应伴随着大量的氧气吸收，这表明HTAU和CSA通过单电子转移机制被氧化为磺酰基自由基，磺酰基自由基可能引发一个以磺酸盐为最终产物的氧依赖性自由基链反应。除了单电子机制外，HTAU和CSA还可以通过双电子途径被氧化，直接生成磺酸盐而不消耗氧气。在pH 7.4和25℃条件下，过氧亚硝酸盐与HTAU和CSA直接反应的表观二级速率常数分别为77.4±5和76.4±9 M⁻¹·s⁻¹。对于这两种亚磺酸盐，表观二级速率常数都随着pH的降低而急剧增加，得到的S形曲线与过氧亚硝酸作为负责亚磺酸盐氧化的物种一致。动力学数据，以及氧气吸收、亚磺酸盐消耗、磺酸盐生成以及亚硝酸盐和硝酸盐产物分布的变化表明，过氧亚硝酸盐对亚磺酸盐的氧化可能通过两种反应途径进行，其相对重要性取决于试剂浓度和pH值。在存在碳酸氢盐的情况下，亚磺酸盐与过氧亚硝酸盐的直接反应受到抑制，氧化反应可能仅涉及过氧亚硝酸盐 - CO₂加合物分解产生的自由基·NO₂和CO₃⁻。
