The objective of this studywas to investigate the biochemical changes of nitric oxide synthase (NOS) in pork skeletal
muscles during postmortem storage. Longissimus thoracis (LT), psoas major (PM) and semimembranosus
(SM) muscles of pork were removed immediately after slaughter and stored under vacuum condition at 4 °C
for 0, 1 and 3 d. Results showed that all threemuscles exhibited NOS activity until 1 d while SM muscle retained
NOS activity after 3 d of storage. The content of nNOS in SM muscle was stable across 3 d of storage while
decreased intensity of nNOS was detected at 1 and 3 d of aging in PM and LT muscles due to the degradation
of calpain. Immunostaining showed that nNOS was located at not only sarcolemma but also cytoplasm at 0
and 1 d of storage.Our data suggest that postmortemmuscles possessNOS activity and nNOS expression depends
on muscle type.