Consonni R, Falanga A, Barbui T
Haematology Division, Ospedali Riuniti Bergamo, Italy.
Br J Haematol. 1994 Jun;87(2):321-4. doi: 10.1111/j.1365-2141.1994.tb04916.x.
Circulating platelet-aggregating activities have been described by several authors. In a previous study we have confirmed the presence in serum and plasma from patients with thrombotic thrombocytopenic purpura (TTP) of a platelet aggregating cysteine proteinase (PACP). This activity differed in that, among the class of thiol enzymes, it showed characteristics of a lysosomal cathepsin rather than of a cytoplasmic calpain. To further investigate the enzymatic properties of this PACP we have designed a study to evaluate the dependence of the activity on Ca++. Calcium-dependence is a property of calpains but not of cathepsins. A proteolytic assay was set up and conducted with and without Ca++. The release of acid-soluble peptide from denatured human globin promoted by TTP samples and standards was fluorimetrically measured. The results show that TTP samples were equally active with and without Ca++ similar to standard papain (the cathepsin B-like proteinase), whereas standard calpain only acted with Ca++. An inhibition study performed by the proteolytic assay confirmed the same pattern of sensitivity of PACP to a series of specific cystein proteinase inhibitors previously shown by the proaggregating assay. The enzymatic behaviour of PACP of TTP resembled a lysosomal (cathepsins) rather than a cytoplasmic (calpains) cysteine proteinase.
几位作者描述了循环血小板聚集活性。在先前的一项研究中，我们已证实在血栓性血小板减少性紫癜（TTP）患者的血清和血浆中存在一种血小板聚集半胱氨酸蛋白酶（PACP）。这种活性的不同之处在于，在硫醇酶类别中，它表现出溶酶体组织蛋白酶的特征，而非胞质钙蛋白酶的特征。为了进一步研究这种PACP的酶学特性，我们设计了一项研究来评估其活性对Ca++的依赖性。钙依赖性是钙蛋白酶的特性，而非组织蛋白酶的特性。我们建立了一种蛋白水解测定法，并分别在有和没有Ca++的情况下进行测定。通过荧光法测量由TTP样本和标准品促进的变性人球蛋白中酸溶性肽的释放。结果显示，TTP样本在有和没有Ca++的情况下活性相同，类似于标准木瓜蛋白酶（组织蛋白酶B样蛋白酶），而标准钙蛋白酶仅在有Ca++时起作用。通过蛋白水解测定法进行的抑制研究证实了PACP对一系列特定半胱氨酸蛋白酶抑制剂的敏感性模式与先前在促聚集测定中显示的相同。TTP的PACP的酶学行为类似于溶酶体（组织蛋白酶）而非胞质（钙蛋白酶）半胱氨酸蛋白酶。
