Tuan R S
Biochem J. 1985 Apr 1;227(1):317-26. doi: 10.1042/bj2270317.
The Ca2+-binding protein (HCaBP) of the human placenta was studied with respect to its biochemical properties, tissue and cellular distribution, and possible involvement in placental Ca2+ transport. Optimal Ca2+ binding by the HCaBP occurs at pH 7-8 and in 100 mM-Na+ and 3 mM-Ca2+. The HCaBP possesses at least 10 Ca2+-binding sites with a Kd of 5 X 10(-6) M ([Ca2+]). Highly specific rabbit-derived anti-HCaBP antibodies were used for HCaBP immunoquantification and immunohistochemistry, which revealed that the HCaBP is localized in the chorionic villi and is primarily associated with the trophoblastic cells of the placenta. In addition, an 'in vitro' cell-free assay system for Ca2+ uptake was constructed with microsomal membranes isolated from term placental tissues. Ca2+ uptake by the placental microsomal fraction exhibited characteristics indicative of active Ca2+ transport such as temperature-dependence, saturability and energetic requirement. In this system, preincubation of microsomal membranes with anti-HCaBP antibodies inhibited Ca2+ uptake, suggesting that the HCaBP is functionally involved in placental membrane Ca2+ uptake.
对人胎盘的钙离子结合蛋白（HCaBP）的生化特性、组织和细胞分布及其在胎盘钙离子转运中的可能作用进行了研究。HCaBP的最佳钙离子结合发生在pH 7 - 8以及100 mM - Na⁺和3 mM - Ca²⁺条件下。HCaBP至少拥有10个钙离子结合位点，解离常数Kd为5×10⁻⁶ M（[Ca²⁺]）。使用高度特异性的兔源抗HCaBP抗体进行HCaBP免疫定量和免疫组织化学分析，结果显示HCaBP定位于绒毛膜绒毛，主要与胎盘的滋养层细胞相关。此外，利用从足月胎盘组织分离的微粒体膜构建了一个用于钙离子摄取的“体外”无细胞检测系统。胎盘微粒体部分的钙离子摄取表现出如温度依赖性、饱和性和能量需求等表明主动钙离子转运的特征。在该系统中，微粒体膜与抗HCaBP抗体预孵育会抑制钙离子摄取，这表明HCaBP在功能上参与胎盘膜的钙离子摄取。
