The reaction between GSNO and H 2 S: On the generation of NO, HNO and N 2 O.

Several recent reports suggest that HNO may be produced endogenously by reaction of H ₂ S and S-nitrosoglutathione (GSNO). This hypothesis was tested using deoxymyoglobin (MbFe ^II ) to trap the expected HNO released from the target reaction, which should generate the stable HNO adduct, HNO-Mb, under anaerobic conditions. Under numerous experimental conditions, the sole globin product was NO-Mb, as characterized by absorbance, EPR, and NMR spectroscopies. Analogous reactions of GSNO with other biological reductants such as ascorbic acid, dithiothreitol, glutathione, and dithionite also yielded NO-Mb as the sole globin product; however, whereas analogous reduction of GSNO using NaBH ₄ generates HNO-Mb in high yield. Quantitative GC/MS analyses of reactions of GS ¹⁵ NO with H ₂ S showed that the main reaction product was ¹⁵ NO, with ¹⁵ N ₂ produced at a comparable level to ¹⁵ N ₂ O. Overall yield of N ₂ O is unchanged by the presence of MbFe ^II , discounting the intermediacy of either NO or HNO in its formation. Taken together, these results argue against the generation of free HNO as a major pathway in the reactions of GSNO with H ₂ S, and instead imply some as yet uncharacterized intermediates generate the nitrogenic gases.
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