Makita K, Shimoyama T, Sakurai Y, Yagi H, Matsumoto M, Narita N, Sakamoto Y, Saito S, Ikeda Y, Suzuki M, Titani K, Fujimura Y
Department of the 2nd Internal Medicine of Nara Medical University, Japan.
Int J Hematol. 1998 Oct;68(3):297-310. doi: 10.1016/s0925-5710(98)00080-2.
Human placental ecto-ATP diphosphohydrolase (ATPDase), an 82 kDa single-chain glycoprotein, was purified to high specific activity using a specific murine monoclonal antibody MK33 (IgG1-kappa). Structurally, protein-based analysis showed this enzyme to be almost identical to that of CD39 lymphoid cell activation antigen deduced by cDNA sequencing (Maliszewski CR, et al, J Immunol 1994; 153:3574); but differing in the NH2-terminal amino acid sequence, suggesting that placental ecto-ATPDase is most likely an isoform of CD39 generated by alternative splicing of the pre-mRNA. Functionally, placental ecto-ATPDase totally inhibits the secondary platelet aggregation induced by agonists at a final concentration (f.c.) of 1 microgram/ml. The purified enzyme (1 microgram/ml, final), pre-incubated with washed platelets prior to alpha-thrombin stimulation, completely inhibits the activation of platelet glycoprotein (GP) IIb/IIIa, thereby blocking the binding of fibrinogen or von Willebrand factor to platelets. Further, under different shear stresses, the enzyme modulates platelet aggregation differently. Low shear stress-induced platelet aggregation is blocked by this enzyme in a dose-dependent manner and is totally blocked at f.c. 0.5 microgram/ml. Under high shear stress, however, this protein at a f.c. of 0.5 microgram/ml mediates almost complete disaggregation of platelets without affecting the initial aggregation. Using immunohistochemical analysis, this enzyme was observed to be localized at the syncytiotrophoblasts of placental microvilli and the endothelial cells (ECs) of the umbilical vein obtained at full-term normal delivery, but scarcely at the ECs of the umbilical artery.
人胎盘ecto - ATP二磷酸水解酶（ATPDase）是一种82 kDa的单链糖蛋白，使用特异性鼠单克隆抗体MK33（IgG1 - κ）纯化至高比活性。在结构上，基于蛋白质的分析表明该酶与通过cDNA测序推导的CD39淋巴细胞活化抗原几乎相同（Maliszewski CR等人，《免疫学杂志》1994年；153:3574）；但在NH2末端氨基酸序列上有所不同，这表明胎盘ecto - ATPDase很可能是由前体mRNA的可变剪接产生的CD39的一种同工型。在功能上，胎盘ecto - ATPDase在终浓度（f.c.）为1微克/毫升时完全抑制激动剂诱导的继发性血小板聚集。纯化的酶（终浓度1微克/毫升）在α - 凝血酶刺激前与洗涤过的血小板预孵育，可完全抑制血小板糖蛋白（GP）IIb/IIIa的活化，从而阻断纤维蛋白原或血管性血友病因子与血小板的结合。此外，在不同的剪切应力下，该酶对血小板聚集的调节方式不同。低剪切应力诱导的血小板聚集被该酶以剂量依赖性方式阻断，在终浓度0.5微克/毫升时完全被阻断。然而，在高剪切应力下，终浓度为0.5微克/毫升的这种蛋白质介导血小板几乎完全解聚，而不影响初始聚集。使用免疫组织化学分析，观察到该酶定位于足月正常分娩时获得的胎盘微绒毛的合体滋养层细胞和脐静脉的内皮细胞（ECs），但在脐动脉的ECs中几乎没有。
