Effect of postmortem storage on activity of μ- and m-calpain in five bovine muscles

J. P. Camou, J. A. Marchello, V. F. Thompson, S. W. Mares, D. E. Goll

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    54 Scopus citations

    Abstract

    An in situ system involving incubation of 60- to 80-g pieces of muscle at 4°C under different conditions was used to determine the effects of time of postmortem storage, of pH, and of temperature on activities of μ- and m-calpain activity in bovine skeletal muscle. Casein zymograms were used to allow measurement of calpain activity with a minimum of sample preparation and to ensure that the calpains were not exposed to ionic strengths of 100 or greater before assay of their activities. In 4 of the 5 muscles (longissimus dorsi, lumbar; longissimus dorsi, thoracic; psoas major; semimembranosus; and triceps brachii) studied, μ-calpain activity decreased nearly to zero within 48 h postmortem. Activity of m-calpain also decreased in the in situ system used but at a much slower rate. Activities of both μ- and m-calpain decreased more slowly in the triceps brachii muscle than in the other 4 muscles during postmortem storage. Although previous studies have indicated that μ-calpain but not m-calpain is proteolytically active at pH 5.8, these studies have used calpains obtained from muscle at death. Both μ- and m-calpain are proteolytically inactive if their activities are measured at pH 5.8 and after incubating the muscle pieces for 24 h at pH 5.8. Western analysis suggested that neither the large 80-kDa subunit nor the small 28-kDa subunit of m-calpain was autolyzed during postmortem storage of the muscle pieces. As has been reported previously, the 80-kDa subunit of μ-calpain was autolyzed to 78- and then to a 76-kDa polypeptide after 7 d postmortem, but the 28-kDa small subunit was not autolyzed; hence, the autolyzed μ-calpain molecule in postmortem muscle is a 76-/28-kDa molecule and not a 76718-kDa molecule as previously assumed. Because both subunits were present in the postmortem calpains, loss of μ-calpain activity during postmortem storage is not due to dissociation of the 2 subunits and inactivation. Although previous studies have shown that the 76-/18-kDa μ-calpain molecule is completely active proteolytically, it is possible that the 76728-kDa μ-calpain molecule in postmortem muscle is proteolytically inactive and that this accounts for the loss of μ-calpain activity during postmortem storage. Because neither μ- nor m-calpain is proteolytically active at pH 5.8 after being incubated at pH 5.8 for 24 h, other proteolytic systems such as the caspases may contribute to postmortem proteolysis in addition to the calpains.

    Original languageEnglish (US)
    Pages (from-to)2670-2681
    Number of pages12
    JournalJournal of animal science
    Volume85
    Issue number10
    DOIs
    StatePublished - Oct 2007

    Keywords

    • Meat tenderness
    • Postmortem muscle
    • Zymogram
    • m-calpain
    • μ-calpain

    ASJC Scopus subject areas

    • Food Science
    • Animal Science and Zoology
    • Genetics

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