Info

Wavelength (nm)

Fig. 2. The UV VIS spectrum of 0.5 mM GSNO in buffer (pH = 7.4). O.D. refers to optical density.

A typical stock of CySNO is obtained by adding equimolar amounts (ca 50 mM) of CySH and sodium nitrite to 0.1 M HCl. The reaction is rather fast and requires less than a minute to complete. The kinetics of CysNO formation at various pH can be seen in Fig. 3. The reaction products always appear as a mixture of CysNO and disul des, with the relative balance being strongly dependent on pH (cf Table 2). At physiological pH the disul de is dominant, but at pH ~ 1 the CysNO yield is nearly 100%. Near pH = 1, the conversion of Cys to CysNO is completed within a minute at 37°C, at room temperature within a few minutes.

As S-nitrosothiols are prone to photolysis and thermolysis, the reaction should proceed in a dark and cool location. The formation of CysNO and GSNO is indicated by its intense

Fig. 3. Kinetics of CysNO formation from acid reduction of nitrite as measured by the optical absorbance at 543 nM in buffered solutions. The starting concentrations were 40 mM CysH and 40 mM nitrite. The temperature was 37°C. (From Ref. [18].)

Tune (min)

Fig. 3. Kinetics of CysNO formation from acid reduction of nitrite as measured by the optical absorbance at 543 nM in buffered solutions. The starting concentrations were 40 mM CysH and 40 mM nitrite. The temperature was 37°C. (From Ref. [18].)

Table 2 Yields of CysNO and cystine obtained in a reaction mixture of 0.04 M CysH with 0.04 M NaNO2 in aqueous buffers at 37°C. The yields show that all cysteine is incorporated in either S-nitrosothiol or the cystine disul de. Data adapted from Ref. [18]

pH

0 0

Post a comment