Nitric oxide synthase in beef semimembranosus muscle during postmortem aging.

In this study, the activity, expression and localization of nitric oxide synthase (NOS) was investigated in beef semimembranosus muscle (SM) during postmortem aging. Five beef SM muscles were vacuum-packaged and aged for 1, 3, 7 and 14 d at 4 °C. Results showed that SM muscle retained NOS activity during the 14 d storage period. Compared to 1 d of storage, NOS activity and neuronal NOS (nNOS) content decreased significantly at 3 and 7 d (P < 0.05). Calpain played a major role in degrading nNOS during beef postmortem aging. In addition, immunofluorescence studies suggested that nNOS in beef SM muscle was mainly distributed in the sarcolemma. The S-nitrosothiol (SNO) content in SM muscle increased significantly at 1, 3 and 7 d post-slaughter. This manuscript is the first study to demonstrate the activity and expression of NOS in beef during postmortem aging.