The reaction between GSNO and H2S: On the generation of NO, HNO and N2O.

Several recent reports suggest that HNO may be produced endogenously by reaction of H2S and S-nitrosoglutathione (GSNO). This hypothesis was tested using deoxymyoglobin (MbFeII) 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 NaBH4 generates HNO-Mb in high yield. Quantitative GC/MS analyses of reactions of GS15NO with H2S showed that the main reaction product was 15NO, with 15N2 produced at a comparable level to 15N2O. Overall yield of N2O is unchanged by the presence of MbFeII, 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 H2S, and instead imply some as yet uncharacterized intermediates generate the nitrogenic gases.