Biochemical investigations into the absence of rigor mortis in the Norway lobster Nephrops norvegicus

It was found that the striated muscle of the Norway lobster (Nephrops norvegicus) does not exhibit the rigor mortis state otherwise typical for this type of muscle. This absence of rigor was investigated, concentrating on changes in the structure, ultrastructure and post-mortem biochemistry of the muscle. Samples were initially fixed for light and electron microscopy at the time of death and at different times post-mortem (3, 6, 12 and 24 h). Protein extracts were obtained in parallel to compare the banding patterns of the myofibrillar proteins using SDS-PAGE. A Western blot was applied to elucidate if myosin – a representative major myofibrillar protein – was degraded post-mortem. And finally, ATP levels in the muscle were analyzed using HPLC. Using TEM imaging it was found that between 12 and 24 h post-mortem at a storage temperature of 10 °C, when rigor mortis should set in (according to the muscular ATP concentrations), an extensive, but rather specific breakdown of myofibrillar proteins occurred. The Z-disks were degraded and the myofibrillar structure was lost. SDS-PAGE and Western blot clearly demonstrated the post-mortem breakdown of myosin. The nature of the observed protein breakdown seems to impede rigor mortis in some way by the activation of at least one of the several proteolytic systems (cathepsins, calpains and others) found in vertebrates and invertebrates. It is speculated that the proteolysis simply overtakes the rigor-inducing post-mortem changes.