在理解导致牛磺酸的半胱氨酸途径的最后步骤中涉及的氧化机制方面已经取得了相当大的进展。亚硫酸盐的氧化,次牛磺酸和半胱氨酸亚磺酸,对各自的磺酸盐,牛磺酸和半胱氨酸,从未与任何特定的酶有关。相反,有强有力的证据表明,在体内形成的牛磺酸和半胱氨酸是亚磺酸与各种生物相关的氧化剂相互作用的结果。在过去的十年里,已经进行了许多实验来了解过氧亚硝酸盐,二氧化氮和碳酸根阴离子可以包括在能够氧化亚磺酸盐的生物相关反应性物种中。多亏了这项工作,有可能强调亚磺酸盐与活性氧和氮物种的两种可能的反应机理(直接和间接反应)。亚硫酸盐氧化,由过氧亚硝酸盐介导,是两种反应机理的一个例子:通过与过氧亚硝酸盐的双电子直接反应或通过单电子间接转移反应。在间接机制中,过氧亚硝酸盐同解释放羟基和二氧化氮自由基,此外,过氧亚硝酸盐和CO2形成的短寿命加合物的降解可以产生碳酸根阴离子。次牛磺酸和半胱氨酸亚磺酸与过氧亚硝酸盐衍生的自由基的反应伴随着大量的氧气吸收,并产生瞬时中间体,它可以通过与磺酸盐的氧依赖机制开始反应,牛磺酸,和作为最终产品的半胱酸。由于脉冲辐射分解研究,已经表明,通过单电子转移反应在两种亚磺酸盐的氧化过程中产生了瞬时磺酰基自由基(RSO2•)。目的是通过近年来从我们实验室获得的结果,分析亚牛磺酸和半胱氨酸亚磺酸亚磺酸亚氨基氧化中反应机理的各个方面。
Considerable strides have been made in understanding the oxidative mechanisms involved in the final steps of the cysteine pathway leading to taurine. The oxidation of
sulfinates, hypotaurine and cysteine sulfinic acid, to the respective sulfonates, taurine and cysteic acid, has never been associated with any specific enzyme. Conversely, there is strong evidence that in vivo formation of taurine and cysteic acid is the result of sulfinate interaction with a variety of biologically relevant oxidants. In the last decade, many experiments have been performed to understand whether peroxynitrite, nitrogen dioxide and carbonate radical anion could be included in the biologically relevant reactive species capable of oxidizing
sulfinates. Thanks to this work, it has been possible to highlight two possible reaction mechanisms (direct and indirect reaction) of
sulfinates with reactive oxygen and nitrogen species.The
sulfinates oxidation, mediated by peroxynitrite, is an example of both reaction mechanisms: through a two-electron-direct-reaction with peroxynitrite or through a one-electron-indirect-transfer reaction. In the indirect mechanism, the peroxynitrite homolysis releases hydroxyl and nitrogen dioxide radical and in addition the degradation of short-lived adduct formed by peroxynitrite and CO2 can generate carbonate radical anion. The reaction of hypotaurine and cysteine sulfinic acid with peroxynitrite-derived radicals is accompanied by extensive oxygen uptake with the generation of transient intermediates, which can begin a reaction by an oxygen-dependent mechanism with the sulfonates, taurine, and cysteic acid as final products. Due to pulse radiolysis studies, it has been shown that transient sulfonyl radicals (RSO2•) have been produced during the oxidation of both
sulfinates by one-electron transfer reaction.The purpose is to analyze all the aspects of the reactive mechanism in the sulfinic group oxidation of hypotaurine and cysteine sulfinic acid through the results obtained from our laboratory in recent years.