Fig. 1.

(A) Strategy for enriching and site-specific identification of SSG-modified Cys-peptides. Ascorbate coupled with CuCl was used for selective reduction of SNO. NEM was used to alkylate free thiols. The cocktail of Grx, GSH, GR, and NADPH was used for selectively reducing protein-SSG. iTRAQ labeling of enriched Cys-peptides was carried out on-resin, followed by DTT elution. (B) Experimental strategy for multiplex quantification of SSG-modified peptides. Cells were treated by different doses of exogenous stimuli. After on-resin iTRAQ labeling, the eluted peptides are subjected to either SDS-PAGE or combined for LC-MS/MS analyses.