Signaling by sulfur-containing molecules. Quantitative aspects

Nitrosopersulfide (SSNO − ) decomposes in the presence of sulfide, cyanide or glutathione to give HSNO/SNO − : consequences for the assumed role in cell signalling

“…The reaction took place due to the fact that under this experimental condition there is a surface-catalysed NO disproportionation and O, which suggests that HNO was generated in between (equation (3.7)), confirming our previous findings from the buffered solutions [13]. Although reaction between HSNO and H 2 S to give HNO (equation (3.7)) is thermodynamically unfavourable (D rxn G 00 ¼ þ32 kJ mol 21 ) [60], if the products get removed/ decomposed (e.g. considering the dimerization of HNO to N 2 O (equation (3.8)), the reaction of HNO with RSH or H 2 S 2 decomposition) reaction could be physiologically relevant.…”

“…Furthermore, it is very important to separate the physiological relevance of all these proposed reactions from those that are just possible in vitro. Considering the very low HS 2 concentration [65,66] and very high thiol concentrations, the reaction shown in equation (3.10) is less likely to occur (although the rate constant for that reaction is approximately 10 7 M 21 s 21 [60]), let alone form HS À 2 , which is intrinsically unstable [67,68] and could easily be reduced by the intracellular thiol pool, and wait to meet another S-nitrosothiol (or, even less probable, another HSNO) to form SSNO 2 . HSNO/SNO 2 remains therefore the most probable signalling molecule able to react with the abundant thiol pool to either cause further trans-nitrosation or HNO and RSS 2 formation, in specific protein environments [69].…”

Inorganic Reactive Sulfur-Nitrogen Species: Intricate Release Mechanisms or Cacophony in Yellow, Blue and Red?

“…Using the results of pulse radiolysis from Filipovic et al [9], Koppenol and Bounds have therefore estimated the rate constant of the reaction between HSNO and HS − (leading to formation of HSS − and HNO) to be 10 7 M −1 ·s −1 . Based on physiological concentrations of • NO and H 2 S and their mutual interaction, they have also predicted that the rate of SSNO − formation could be only ~10 −14 M −1 ·s −1 [47]. Together, these kinetic parameters indicate that SSNO − production under such conditions is not biologically relevant.…”

“…Even worse, GSH is quite abundant and occurs in cells, tissues or blood at millimolar concentrations. Since GSH can react with disulfide to form glutathione persulfide and HS − , it can further lower the SSNO − yield [12,47]. …”

Inorganic hydrogen polysulfides: chemistry, chemical biology and detection

“…The estimated Gibbs energies of formation of H 2 S 2 Δ f G o (H 2 S 2 ) are −2 kJ·mol −1 in the gas phase and +5 kJ·mol −1 in water. From the Δ f G o values for HSSH, HSS − and SS 2− , a p K a of 2.6 is estimated for HSSH, and a p K a of 13 is estimated for HSS − (Koppenol and Bounds, ).…”