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钙蛋白酶广泛存在于各组织，广泛表达的钙蛋白酶有两种，钙蛋白酶Ⅰ和钙蛋白酶Ⅱ，它们激活所需的Ｃａ２＋浓度不同．这两种酶都有大、小两个亚基，分子质量分别为８０ｋｕ和３０ｋｕ．大亚基有４个结构域，小亚基由２个结构域构成．新近还发现了几种组织特异表达的钙蛋白酶．钙蛋白酶抑制蛋白是钙蛋白酶的内源抑制蛋白，它由５个结构域组成，其中４个为重复序列，均具有独立抑制钙蛋白酶活性的功能．体内钙蛋白酶活性受到严格调控，贴膜反应可以降低钙蛋白酶对Ｃａ２＋的依赖性，膜磷脂头部所带的磷酸基团与激活作用有关，自溶也可以降低对Ｃａ２＋的依赖，而钙蛋白酶抑制蛋白则起专一的抑制作用．
Calpain is widely present in various tissues. There are two widely expressed calpains, calpain I and calpain II, which require different concentrations of Ca2 + for their activation. Both enzymes have large and small two subunits, molecular weights were 80ku and 30ku. Large subunits have 4 domains, small subunits consist of 2 domains. Recently, several tissue-specific calpains have also been found. Calpastatin is the endogenous inhibitory protein of calpain. It consists of five domains, of which four are repetitive sequences and all have the function of independently inhibiting calpain activity. Tissue calpain activity is strictly regulated, and the membrane reaction can reduce the dependence of calpain on Ca2 +. The phosphoryl group carried by the head of membrane phospholipid is related to activation, autolysis can also reduce the dependence on Ca2 +, and calpastatin Then play a special role in the inhibition.