Carsten M E
J Gen Physiol. 1969 Apr;53(4):414-26. doi: 10.1085/jgp.53.4.414.
The binding of calcium by isolated sarcoplasmic reticulum from cow uterus was studied. Sarcoplasmic reticulum was prepared by differential centrifugation. Three fractions were obtained: I, sedimented between 2,500-15,000 x g; II at 40,000 x g; and III, at 150,000 x g. Fraction II was further purified on a sucrose density gradient. All three fractions contained considerable amounts of intrinsic calcium, mostly in fraction I. Calcium binding in the presence of ATP(1) and Mg also was greatest in fraction I, followed by fraction II, with less in fraction III. Without ATP no calcium was taken up. 5 and 10 mM sodium azide partially inhibited calcium binding in fraction I, but not in fraction II, suggesting the presence of some mitochondria or mitochondrial fragments in fraction I. Calcium binding in fraction II was completely inhibited by 3 mM salyrgan; this fraction thus appears to be sarcoplasmic reticulum. ATPase activity was found in all three fractions, highest in fraction II. It is computed that calcium binding in fractions I and II, on the basis of a 50% yield of protein, is sufficient to elicit contraction by supplying calcium to the contractile proteins of the smooth muscle cell and to regulate relaxation and contraction.
对从母牛子宫分离出的肌浆网与钙的结合进行了研究。通过差速离心制备肌浆网。得到了三个组分：组分I，在2500 - 15000×g之间沉淀；组分II，在40000×g沉淀；组分III，在150000×g沉淀。组分II在蔗糖密度梯度上进一步纯化。所有三个组分都含有相当数量的内源性钙，大部分存在于组分I中。在ATP(1)和镁存在的情况下，钙结合在组分I中也最大，其次是组分II，组分III中较少。没有ATP时不摄取钙。5和10 mM叠氮化钠部分抑制组分I中的钙结合，但不抑制组分II中的，这表明组分I中存在一些线粒体或线粒体片段。3 mM汞撒利完全抑制组分II中的钙结合；因此该组分似乎是肌浆网。在所有三个组分中都发现了ATP酶活性，在组分II中最高。据计算，基于50%的蛋白质产量，组分I和II中的钙结合足以通过向平滑肌细胞的收缩蛋白供应钙来引发收缩，并调节舒张和收缩。
