Characterization and purification of a Ca2+ ion-activated neutral proteinase inhibitor in rabbit skeletal muscle

Modelling post-mortem tenderisation-III: Role of calpain I in conditioning

A simple model is developed to show how proteolysis by calpain I can account for the variations in tenderness in electrically stimulated and nonstimulated beef pectoralis profundus muscles stored between 0°C and 30°C. As the pH of the muscle falls to about 6·1, calpain I is activated and causes proteolysis and tenderisation. The rate of tenderisation is then proportional to the concentration of calpain I which is autolysed slowly reducing its concentration and the rate of tenderisation. The activation energy for the inactivation (autolysis) of calpain I is slightly higher than that for its activity in tenderisation (proteolysis) and therefore, at higher temperatures, less tenderisation occurs. Proteolysis and tenderisation continue at a rate governed by the concentration of calpain I and the temperature until calpain I is depleted when tenderisation stops. Parameters for the activity and inactivation of calpain I were derived and were shown to predict 68% of the variation in toughness.

Myoblast migration is regulated by calpain through its involvement in cell attachment and cytoskeletal organization

Cell migration is a fundamental cellular function particularly during skeletal muscle development. Ubiquitous calpains are well known to play a pivotal role during muscle differentiation, especially at the onset of fusion. In this study, the possible positive regulation of myoblast migration by calpains, a crucial step required to align myoblasts to permit them to fuse, was investigated. Inhibition of calpain activity by different pharmacological inhibitors argues for the involvement of these proteinases during the migration of myoblasts. Moreover, a clonal cell line that fourfold overexpresses calpastatin, the endogenous inhibitor of calpains, and that exhibits deficient calpain activities was obtained. The results showed that the migratory capacity of C2C12 and fusion into multinucleated myotubes were completely prevented in these clonal cells. Calpastatin-overexpressing myoblasts unable to migrate were characterized by rounded morphology, the loss of membrane extensions, the disorganization of stress fibers and exhibited a major defect in new adhesion formation. Surprisingly, the proteolytic patterns of desmin, talin, vinculin, focal adhesion kinase (FAK) and ezrin, radixin, moesin (ERM) proteins are the same in calpastatin-overexpressing myoblasts as compared to control cells. However, an important accumulation of myristoylated alanine-rich C kinase substrate (MARCKS) was observed in cells showing a reduced calpain activity, suggesting that the proteolysis of this actin-binding protein is calpain-dependent and could be involved in both myoblast adhesion and migration.

Calpain-PKC inter-relations in mouse hippocampus: a biochemical approach

In previous studies, we isolated and identified a mu-calpain/PKCalpha complex from rabbit skeletal muscle. Here, we have used specific purification procedures in order to study the interactions between mu-calpain and PKC in mouse hippocampus, a brain structure implicated in memory processes. We observed that mu-calpain and conventional PKCs (alpha, betaII and gamma) are co-eluted after anion exchange chromatography. In contrast to our previous results obtained on skeletal muscle, mu-calpain and PKC isoenzymes were dissociated after gel filtration chromatography. Furthermore, mu-calpain induced the proteolytic conversion of PKCalpha, betaII, and gamma into PKMalpha, betaII, and gamma with a preferential hydrolysis of PKCgamma, a specific isoenzyme of the nervous system. Although the mu-calpain/PKC interactions in the hippocampus are quite different from skeletal muscle, our results however, point out the functional importance of these inter-relations. Moreover, as PKCgamma has been involved in the biochemical events underlying learning and memory, the preferential relationship between mu-calpain and PKCgamma promotes the importance of the role that mu-calpain could play in the cellular mechanisms of memory formation.

Tissue distribution of an endogenous inhibitor of calcium-activated neutral protease and age-related changes in its activity in rats

1. The distribution of an endogenous inhibitor of calcium-activated neutral protease (CANP) and age-related changes in its activity were studied in male and female rats of different ages by a fluorometric assay on tissue extracts after heat treatment. 2. Ubiquitous distribution of CANP inhibitor in brain, cardiac muscle, lung, spleen, liver, skeletal muscle, kidney and testis and its abundance in spleen, liver and kidney was demonstrated. 3. Comparison in terms of units/ml of crude extracts showed that the level of CANP inhibitor exceeded that of CANP in most tissues and that the relative content of CANP inhibitor to mCANP and microCANP differed greatly among tissues. 4. Sex and species differences in CANP inhibitor activity in each tissue were of little significance. 5. Changes in CANP inhibitor during aging from 6 to 12 months was not obvious but senescent rats showed a tendency toward increased inhibitor activity. This increase was especially evident in the testis.

Characterization of calpains and calpastatins from hamster skeletal muscle

1. Hamster skeletal muscle contains a wide-specificity calpain which was found to be a calpain II type and which is composed of a single Mr 80,000 polypeptide. 2. The muscle also contains a calpain I type enzyme which is specific for desmin degradation, and this enzyme consists of a single subunit of Mr 67,000. 3. Three calpastatins were detected in the tissue, one of which inhibited both calpains, whereas the other two appeared to be specific for the desmin-specific calpain. These calpastatins possessed the same inhibition properties when assayed with chicken gizzard calpains.

Purification of a high-molecular-weight inhibitor of the calcium-activated proteinase

An inhibitor of the muscle calcium-activated proteinases has been purified from porcine skeletal muscle by using DEAE-cellulose column chromatography, thermal treatment, Sephacryl S-400 column chromatography in 6 M urea and Sephacryl S-300 column chromatography in 6 M urea. Sodium dodecyl sulfate polyacrylamide slab gel electrophoresis shows that the purified inhibitor is homogeneous and has a subunit molecular weight of 172 000. The inhibitor inactivates both the low- and high-calcium-requiring forms of the calcium-activated proteinase but does not inhibit other proteinases against which it has been tried. It thus appears that the inhibitor is specific for the calcium-activated proteinase. Studies using homogeneous inhibitor and high-calcium-requiring proteinase show that one molecule of the inhibitor can inactivate up to eight molecules of the calcium-activated proteinase. Inactivation of the calcium-activated proteinase by the inhibitor cannot be reversed by calcium concentrations as high as 25 mM, thus eliminating the possibility that the inhibitor functions by chelating calcium. The inhibitory peptide appears to be extremely susceptible to proteolysis during its isolation. Even in the presence of synthetic proteinase inhibitors different inhibitor preparations yield homogeneous inhibitory peptides ranging in molecular weight from 145 000 to 172 000. Preparative electrophoresis and column chromatography have been used to isolate putative proteolytic breakdown products of the 172 kDa peptide at 145, 114, 41 and 29 kDa.

Molecular diversity of calpastatin in mammalian organs

The crude homogenates of various human and porcine organs were subjected to immunoelectrophoretic blot analysis using affinity-purified anti-calpastatin antibody which specifically reacts with human erythrocyte 70 kDa calpastatin. Multiple immuno-reactive bands were revealed which ranged from 100 to 50 kDa. The results indicated the diversity of monomeric calpastatin molecules. The band patterns were different from one organ to the other. Among them, lung, heart and skeletal muscle were characterized by the predominance of 90-100 kDa calpastatin, having a common antigenicity to erythrocyte 70 kDa calpastatin. Such molecular diversity of calpastatins was also substantiated by enzymatic and chromatographic analyses.