Imamura Y, Kawakita M
J Biochem. 1986 Jul;100(1):133-41. doi: 10.1093/oxfordjournals.jbchem.a121685.
Sarcoplasmic reticulum membranes were treated with trypsin under conditions leading to accumulation of B and three other fragments a little smaller than A1, namely A1a, A1b, and C (Mr 27,000-28,000) (Saito, K. et al. (1984) J. Biochem. 95, 1297-1304), and enzymatic properties of trypsin-digested ATPase were investigated. The tryptic cleavage pattern of SR membranes in the presence of 1 M glycerol and 5 mM CaCl2 at 35 degrees C was qualitatively similar to that obtained in the presence of Ca2+ alone. However, considerably more A1-derived fragments, A1a and A1b, which are stabilized by the binding of Ca2+ to the enzyme, were accumulated. The sample digested under this condition for 60 min was mainly composed of A1b and B, and was designated as A1b + B complex. ATPase activity was lost in parallel with the formation of A1a and A1b. On the other hand, E-P forming activity was still retained by A1b + B complex. E-P formation with this complex was strictly dependent on the presence of Ca2+ ions at micromolar concentration. This indicates that Ca2+ binding site is well conserved in this complex. E-P formed with A1b + B complex was ADP-sensitive (E1-P), and was not further decomposed, since the transition from E1-P to E2-P was blocked.
在导致B以及另外三个比A1略小的片段（即A1a、A1b和C，分子量为27,000 - 28,000）积累的条件下，用胰蛋白酶处理肌浆网膜（斋藤，K.等人（1984年）《生物化学杂志》95卷，1297 - 1304页），并研究了胰蛋白酶消化的ATP酶的酶学性质。在35℃下，在1 M甘油和5 mM氯化钙存在的情况下，肌浆网膜的胰蛋白酶切割模式在质量上与仅在钙离子存在时获得的模式相似。然而，通过钙离子与酶的结合而稳定的、源自A1的片段A1a和A1b积累得更多。在这种条件下消化60分钟的样品主要由A1b和B组成，被命名为A1b + B复合物。ATP酶活性随着A1a和A1b的形成而丧失。另一方面，A1b + B复合物仍然保留了E - P形成活性。该复合物的E - P形成严格依赖于微摩尔浓度的钙离子的存在。这表明钙离子结合位点在该复合物中保存良好。由A1b + B复合物形成的E - P对ADP敏感（E1 - P），并且由于从E1 - P到E2 - P的转变被阻断而不会进一步分解。
