Scheme 5. The kinetic equilibrium between thiol-DNIC and its constituents .
(Fig. 11A,B). However, subsequent addition of 20 mM cysteine completely recovered the EPR signal from Cys-DNIC (Fig. 11C).
The excess free cysteine was consumed during the regeneration of Cys-DNIC from Cys-NO. As described in Chapter 2, the drop in the free cysteine must shift the equilibrium between monomeric and dimeric Cys-DNIC towards the dimeric diamagnetic form. Phrased otherwise, the equilibrium of Scheme 6 is shifted towards left-hand side.
For glutathione, the same reaction equilibria apply as for the cysteine discussed above, albeit with slower reaction rates and lower yields. The yields of GS-DNIC from S-nitrosoglutathione (GS-NO) and ferrous iron in the presence of glutathione were an order
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