Hymel L, Nielsen M, Gietzen K
Biochim Biophys Acta. 1985 May 28;815(3):461-7. doi: 10.1016/0005-2736(85)90374-8.
We have investigated the subunit structure of Ca2+-transport ATPase in human erythrocyte membranes using radiation inactivation analysis. All inactivation data were linear on a semilog plot down to at least 20% of the control activity. We found a target size for the calmodulin-dependent Ca2+-ATPase activity of 331 kDa, consistent with the presence of this enzyme as a dimer in calmodulin-depleted ghosts. Membranes which had been saturated with calmodulin before irradiation yield a a similar size of 317 kDa, implying that activation of Ca2+-transport ATPase by calmodulin does not involve significant change in oligomeric structure. Basal (calmodulin-independent) Ca2+-ATPase activity corresponded to a size of 290 kDa, suggesting that this activity resides in the same, or similar-sized, complex as the calmodulin-dependent activity. Mg2+-ATPase activity, however, was found to reside in a smaller complex of 224 kDa, which proved to be statistically distinct from the target size of Ca2+-ATPase activity. It would appear that Mg2+-ATPase is a distinct entity whose function is likely unrelated to the Ca2+-transport ATPase.
我们使用辐射失活分析研究了人红细胞膜中Ca2+转运ATP酶的亚基结构。所有失活数据在半对数图上呈线性，直至对照活性的至少20%。我们发现钙调蛋白依赖性Ca2+-ATP酶活性的靶标大小为331 kDa，这与该酶在钙调蛋白缺失的血影中以二聚体形式存在一致。在辐照前用钙调蛋白饱和的膜产生的类似大小为317 kDa，这意味着钙调蛋白对Ca2+转运ATP酶的激活不涉及寡聚体结构的显著变化。基础（不依赖钙调蛋白）Ca2+-ATP酶活性对应的大小为290 kDa，表明该活性存在于与钙调蛋白依赖性活性相同或相似大小的复合物中。然而，发现Mg2+-ATP酶活性存在于一个较小的224 kDa复合物中，事实证明该复合物在统计学上与Ca2+-ATP酶活性的靶标大小不同。看来Mg2+-ATP酶是一个独特的实体，其功能可能与Ca2+转运ATP酶无关。
