Calpains and calpastatin from cold-shortened bovine M. longissimus lumborum.

Sections of beef longissimus lumborum from four animals were held after 1 hr post mortem at either 0 ° (cold-shortened) or at 15 °C (controls). After 24 hr, the levels of μ- and m-calpains were the same in both treatments and about 30% and 85% of their initial levels respectively. The level of calpastatin at 24 h was higher in cold-shortened (100%) than in controls (60% of its initial level). During subsequent storage at 4 °C, the activities of calpains and calpastatin decreased similarly in extracts from both cold-shortened and control muscles. The similar levels of μ-calpain during the first 24 hr post mortem but at the lower temperature suggest that there is less activity under cold-shortening conditions. This, combined with the increased calpastatin levels, would produce less proteolysis by the calpain system. Reduced proteolysis is therefore a factor which should be considered in an understanding of the mechanism of cold-shortening toughness.