**15. The mechanism of the dependent Ca++ protease**

The Ca++ dependent protease is of two types: type 1 and type 2: this division is based on the level of Ca++ necessary for their activation. The type 1 isoform is activated in presence of micromolar levels of Ca++, whereas the type 2 form needs quantities in milli- molars for its activation (Murachi et al., 1981). Unlike not for the lysosomal protease, this enzyme has it optimal pH in the field of neutrality. Its activation is associated with the degradation of particular structures inside the myocell and in particular in the degradation of the Z band (Bush et al., 1972; Ishiura et al., 1980), of the myofilaments (Daytona et al., 1976; 1979; Cullen and Fulthorpe, 1982) and of the A band (Friden et al., 1981; Newham et al., 1983; Ogilvie et al., 1988). All these alterations are observable in an injured muscle following eccentric exercise. Also the proteins of the cytoskeleton would represent a preferential underlayer for the action of the Ca++ dependent protease (Pontremoli and Melloni, 1986) To this end, there has been a hypothesis that the proteolysis of the vinculin (a protein of the cytoskeleton which anchors the cellular membrane to the cytoskeleton) on behalf of the Ca++ dependent protease, causes a fragility of the sarco‐ lemma of the myocardium cells in the course of the ischemic process (Steenbergen et al., 1987a).
