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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Meat Safety and Quality » Research » Publications at this Location » Publication #90595
Title: EFFECT OF CALPASTATIN ON DEGRADATION OF MYOFIBRILLAR PROTEINS BY U-CALPAIN UNDER POSTMORTEM CONDITIONS

Author
item Geesink, Gerrit
item Koohmaraie, Mohammad

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Meat tenderness is an important component of meat quality, and inconsistency in meat tenderness has been identified as one of the major problems facing the meat industry. Degradation of structural muscle proteins by calcium dependent neutral proteases (calpains) is responsible for meat tenderization during postmortem storage of meat. The expression of calpain activity is in part regulated by the presence of an inhibitor of the calpains, calpastatin. Calpastatin activity at 24 h postmortem is inversely proportional to postmortem tenderization and accounts for a greater proportion of the variation in beef tenderness (approximately 40%) than any other single variable. In light of the importance of calpain and calpastatin activity in postmortem muscle and meat tenderness, it is important to determine the mechanism of their interaction under conditions observed in postmortem muscle. The objective of the experiments described was to study proteolysis of muscle proteins by calpain in the presence of calpastatin under conditions mimicking postmortem storage of muscle. The results indicated that even in the presence of excess calpastatin, proteolysis of muscle proteins by calpain is not completely inhibited. Furthermore, the extent of proteolysis of muscle proteins is limited by instability of calpain, leading to loss of activity, under conditions observed in postmortem muscle.

Technical Abstract: To improve our understanding of the regulation of u-calpain activity in situ during postmortem storage of muscle, the effect of different calpastatin levels on proteolysis of myofibrillar proteins by u-calpain in a system closely mimicking postmortem conditions was studied. Increasing the amount of calpastatin in the incubations limited both the rate and extent of proteolysis of myofibrillar proteins and autolysis of u-calpain. Excess calpastatin, i.e., a u-calpain to calpastatin ratio of 1 to 4, did not inhibit proteolysis completely, regardless of pH. Western blot analysis revealed that proteolysis of myofibrillar proteins virtually ceased after 7 d of incubation despite the presence of partly autolyzed and, therefore, seemingly active u-calpain. A series of incubations of autolyzed u-calpain revealed that the autolyzed form of this enzyme is unstable at a ionic strength observed in postmortem muscle. The possible significance of these results in terms of the regulation of u-calpain activity in postmortem muscle is discussed.