Martin D W
Biochemistry. 1983 Apr 26;22(9):2276-82. doi: 10.1021/bi00278a034.
Sarcoplasmic reticulum calcium adenosinetriphosphatase (Ca2+-ATPase) was solubilized to monomeric form with the nonionic detergent n-dodecyl octaethylene glycol monoether (C12E8). Equilibrium ultracentrifugation analysis indicated that this preparation is initially greater than 75% monomer, the remainder being best described as a tetramer. In the presence of substrates, this preparation has ATPase activity comparable to that of leaky sarcoplasmic reticulum vesicles. The possibility of substrate-induced oligomerization of the monomer under ATPase activity assay conditions was tested. Active enzyme centrifugation analysis demonstrated that ATPase activity sedimented with a rate which can only be attributed to a monomeric particle. The sedimentation rate was invariant over a 6-fold concentration range comparable to that used in activity assays. The portion of the protein that sediments as an oligomer when measurements are based on the movement of protein (A280) is not seen when measurements are based on the movement of activity. The data demonstrate that the monomer represents the minimal ATPase active unit of Ca2+-ATPase.
肌浆网钙腺苷三磷酸酶（Ca2+-ATP酶）用非离子去污剂正十二烷基八乙二醇单醚（C12E8）溶解成单体形式。平衡超速离心分析表明，该制剂最初大于75%为单体，其余部分最好描述为四聚体。在底物存在的情况下，该制剂的ATP酶活性与有渗漏的肌浆网囊泡相当。测试了在ATP酶活性测定条件下底物诱导单体寡聚化的可能性。活性酶离心分析表明，ATP酶活性以仅可归因于单体颗粒的速率沉降。在与活性测定中使用的浓度范围相当的6倍浓度范围内，沉降速率不变。当基于蛋白质的移动（A280）进行测量时，作为寡聚体沉降的蛋白质部分，在基于活性的移动进行测量时则看不到。数据表明，单体代表Ca2+-ATP酶的最小ATP酶活性单位。
