The calpain system and skeletal muscle growth

The first protein of a group of proteins now identified as belonging to the calpain system was purified in 1976. The calpain system presently is known to be constituted of three well-characterized proteins; several lesser stu died proteins that have been isolated from invertebrates; and 10 mRNAs, two each in Drosophila and C. elegans and six in vertebrates, that encode prot eins, which, based on sequence homology, belong to the calpain family. The three well-characterized proteins in the calpain family include two Ca2+-de pendent proteolytic enzymes, mu-calpain and m-calpain, and a protein, calpa statin, that has no known activity other than to inhibit the two calpains. A substantial amount of experimental evidence accumulated during the past 2 5 yr has shown that the calpain system has an important role both in rate o f skeletal muscle growth and in rate and extent of postmortem tenderization . Calpastatin seems to be the variable component of the calpain system, and skeletal muscle calpastatin activity is highly related to rate of muscle p rotein turnover and rate of postmortem tenderization. The current paradigm is that high calpastatin activity: 1) decreases rate of muscle protein turn over and hence is associated with an increased rate of skeletal muscle grow th; and 2) decreases calpain activity in postmortem muscle and hence is ass ociated with a lower rate of postmortem tenderization. This article summari zes some of the known properties of the calpain system and discusses the po tential importance of the calpain system to animal science.