Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2006
Publication Date: 11/1/2006
Citation: Geesink, G.H., Kuchay, S., Chishti, A.H., Koohmaraie, M. 2006. µ-calpain is essential for postmortem proteolysis of muscle proteins. Journal of Animal Science 84:2834-2840. Interpretive Summary: A large amount of indirect evidence shows that µ-calpain is responsible for the breakdown of structural proteins in postmortem skeletal muscle, and that this degradation is responsible for tenderization of meat. However, research relating µ-calpain activity to postmortem proteolysis will benefit from direct evidence. To this end we have examined postmortem proteolysis in muscles from a strain of mice that had µ-calpain knocked out of its genome and compared proteolysis with that occurring in muscles from normal mice. Results indicate that postmortem proteolysis was largely inhibited in µ-calpain knockout mice. The limited amount of postmortem proteolysis observed in µ-calpain knockout mice could be attributed to m-calpain, which is inactive in postmortem beef and lamb. Thus, the results of this study provide direct evidence that µ-calpain is essential for breakdown of structural proteins in postmortem skeletal muscle. Therefore, understanding the regulation of µ-calpain in postmortem muscle should be the focus of further research on postmortem proteolysis and tenderization of meat.
Technical Abstract: The objective of this investigation was to test the hypothesis that µ-calpain is largely responsible for postmortem proteolysis of muscle proteins. To accomplish this objective, we compared proteolysis of known muscle proteins in muscles of wild type and µ-calpain knockout mice during postmortem storage. Knockout mice (n = 6) were sacrificed along with control mice (n = 6). Hind limbs were removed and stored at 4°C. Muscles were dissected at 0, 1, and 3 d postmortem and subsequently analyzed for degradation of nebulin, dystrophin, metavinculin, vinculin, desmin, and troponin-T. In a separate experiment, hind limb muscles from knockout (n = 4) and control mice (n = 4) were analyzed at 0, 1, and 3 d postmortem using casein zymography to confirm that µ-calpain was knocked out in muscle and to determine whether m-calpain is activated in murine postmortem muscle. Cumulatively, the results of the first experiment indicated that postmortem proteolysis was largely inhibited in µ-calpain knockout mice. The results of the second experiment established the absence of µ-calpain in the muscle tissue of knockout mice, and confirmed results of an earlier study that m-calpain is active in postmortem murine muscle. The results of the present study show that even in a species where m-calpain is activated to some extent postmortem, µ-calpain is largely responsible for postmortem proteolysis. This observation excludes a major role for any of the other members of the calpain family or any other proteolytic system in postmortem proteolysis of muscle proteins. Therefore, understanding the regulation of µ-calpain in postmortem muscle should be the focus of further research on postmortem proteolysis and tenderization of meat.