Rubinoff M J, Nellans H N
J Biol Chem. 1985 Jul 5;260(13):7824-8.
Calcium uptake by an endoplasmic reticulum-enriched membrane fraction isolated from rat small intestine was investigated using a rapid filtration technique. Calcium sequestration was stimulated by the presence of ATP and released by the calcium ionophore A23187. ATP stimulation of calcium uptake was dependent on the presence of magnesium, inhibited by vanadate, and refractory to calmodulin. Kinetic studies revealed a K0.5 for the ATP-stimulated uptake of 62.5 nM Ca and a Jmax of 1.4 nmol of Ca/mg protein X min. A high dietary calcium load stimulated maximal uptake by 80% with no change in affinity. The magnitude of maximal uptake and the high affinity of this transport system suggest that the endoplasmic reticulum may play a significant role in cytosolic calcium sequestration and that extracellular calcium leads to modulation of intracellular endoplasmic reticulum calcium buffering.
利用快速过滤技术研究了从大鼠小肠分离出的富含内质网的膜组分对钙的摄取。ATP的存在刺激了钙的螯合，钙离子载体A23187则使其释放。ATP对钙摄取的刺激依赖于镁的存在，受钒酸盐抑制，且对钙调蛋白不敏感。动力学研究表明，ATP刺激摄取的K0.5为62.5 nM钙，Jmax为1.4 nmol钙/毫克蛋白×分钟。高膳食钙负荷使最大摄取量增加80%，亲和力无变化。该转运系统的最大摄取量和高亲和力表明，内质网可能在胞质钙螯合中起重要作用，细胞外钙会导致细胞内内质网钙缓冲的调节。
