Identification of S-nitrosylated proteins in postmortem pork muscle using modified biotin switch method coupled with isobaric tags

The objective of this study was to identify the S-nitrosylated proteins in aging samples of pork longissimus thoracis muscle (aged 0 and 3 d) and to study the effects of exogenous S-nitrosoglutathione (GSNO, concentration at 10 and 100 mu M) treatments of aged 0 d sample. After validating modified biotin switch method, the samples were labeled with tandem mass tags (TMT126.129) for the LC-MS/MS analysis. A total of 366 peptides were identified to be S-nitrosylated corresponding to 339 proteins. Comparison of total intensity and individual S-nitrosylated sites between aging samples revealed that S-nitrosylation did occur in pork muscle during postmortem aging through possible pathways of denitrosylation and transnitrosylation. GSNO treatment groups showed a considerable number of potential cysteines could be modified with high thiol-reactivity. It was deduced that S-nitrosylation could be involved in the postmortem metabolic process possibly through the regulation of activity or function of glycolytic enzymes, calcium release, heat shock proteins, antioxidant enzymes and myofibrillar proteins.