Oxidation of Hypotaurine and Cysteine Sulfinic Acid by Peroxidase-generated Reactive Species.

Abstract

AbstractHypotaurine (HTAU) and cysteine sulfinic acid (CSA) are the metabolic intermediates in the mammalian pathway leading from cysteine to taurine. Strong evidence has been presented that the formation of taurine (TAU) and cysteic acid (CA) is the result of the interaction of both sulfinates with various oxidizing agents that may be present in biological systems. The purpose of the present study is to investigate the oxidation of sulfinates, HTAU and CSA, by peroxidase-generated reactive species. Reactive nitrogen and oxygen species can be produced during the process of nitrite oxidation catalyzed by heme peroxidases, such as horseradish peroxidase (HRP) or myeloperoxidase, in the presence of hydrogen peroxide (H2O2). Nitrite is the major end product of nitric oxide (NO) metabolism. Oxidation of nitrite by such mechanisms could be important at sites of inflammatory processes. The formation of reactive nitrogen species (RNS) via peroxidase-catalyzed oxidation of nitrite could represent an additional mechanism of the formation of taurine. The oxidation of the sulfinates, HTAU and CSA, by HRP/H2O2/nitrite system has been evaluated by monitoring the oxygen consumption and the production of the corresponding sulfonates, TAU and CA. Moreover, the effect of HTAU and CSA, on nitrotyrosine formation by HRP/H2O2/nitrite system has been studied. During the HRP/H2O2-dependent oxidation of tyrosine, tyrosyl radicals are formed. The results provide evidence that sulfinates inhibit nitrotyrosine formation not only by scavenging RNS but also by reducing the peroxidase-generated tyrosyl radical.KeywordsCysteic acidCysteine sulfinic acidHypotaurineNitrogen dioxidePeroxidaseReactive nitrogen speciesSulfinateSulfonyl radicalTaurineTyrosyl radical