Low molecular thiols, pH and O2 modulate H2S-induced S-nitrosoglutathione decomposition - •NO release

We studied the involvement of O2, pH and low molecular thiols in H2S-induced decomposition of S-nitrosoglutathione (GSNO). The GSNO decomposition - •NO release was evaluated by UV-VIS spectroscopy and Griess assay. The H2S donor Na2S was used. O2 slightly increased, but was not necessary for the H2S-induced GSNO decomposition. The rate of GSNO decomposition depended on pH; the maximum rate was observed at pH 7.4-8.0, and this decreased with lowering pH (6.4-4.5) as well as with increasing pH at 9.0-12.0. H2S-induced GSNO decomposition was slowed by the presence of other thiols, such as L-cysteine (Cys), N-acetyl-L-cysteine (NAC) and L-glutathione (GSH), but not in the presence of L-methionine (Met) or oxidized glutathione (GSSG). In sharp contrast, at pH 6.0, H2S-induced GSNO decomposition was negligible, yet the presence of Cys, NAC and GSH induced the H2S-driven GSNO decomposition (whilst Met and GSSG were inactive). In conclusion we postulate an involvement of low molecular thiols and pH in •NO signaling, by modulating the interactions of H2S with nitroso compounds, and hence in part they also appear to control H2S-triggered •NO release. The interaction of H2S and/or its derivatives with the thiol group may be responsible for the observed effects.