Taylor R G, Christiansen J A, Goll D E
Muscle Biology Group, University of Arizona, Tucson.
Biomed Biochim Acta. 1991;50(4-6):491-8.
The structure of human platelets differs from that of bovine platelets in that human platelets have a surface-connected canalicular system that bovine platelets lack. Platelets are one of the richest known sources of the calpains, and the calpains have been implicated in many of the specific cleavages of cytoskeletal and surface-receptor proteins that occur during platelet activation and aggregation. Several studies have reported that human platelets are rich in mu-calpain and contain less m-calpain, whereas bovine platelets contain principally m-calpain and almost no mu-calpain. The immunolocalization studies reported here show that calpastatin is distributed throughout the cytosol of both human and bovine platelets and that calpain is located throughout the interior of human platelets. Calpain in bovine platelets is located primarily in alpha-granules, however. Because bovine platelets contain predominantly m-calpain and because alpha-granules are translocated to the platelet surface during activation, bovine m-calpain may be responsible for the specific cleavages of platelet surface proteins such as glycoprotein Ib that occur during platelet activation and at extracellular Ca2+ concentrations high enough to activate m-calpain.
人类血小板的结构与牛血小板不同，在于人类血小板有一个表面连接的小管系统，而牛血小板没有。血小板是已知富含钙蛋白酶的来源之一，并且钙蛋白酶与血小板激活和聚集过程中发生的许多细胞骨架和表面受体蛋白的特异性裂解有关。几项研究报告称，人类血小板富含μ-钙蛋白酶且含较少的m-钙蛋白酶，而牛血小板主要含m-钙蛋白酶且几乎不含μ-钙蛋白酶。此处报告的免疫定位研究表明，钙蛋白酶抑制蛋白分布在人类和牛血小板的整个细胞质中，并且钙蛋白酶位于人类血小板的整个内部。然而，牛血小板中的钙蛋白酶主要位于α-颗粒中。由于牛血小板主要含有m-钙蛋白酶，并且由于α-颗粒在激活过程中会转移到血小板表面，因此牛m-钙蛋白酶可能是血小板激活期间以及细胞外Ca2+浓度高到足以激活m-钙蛋白酶时发生的血小板表面蛋白（如糖蛋白Ib）特异性裂解的原因。
