Aderem A A, McIntosh D B, Berman M C
Proc Natl Acad Sci U S A. 1979 Aug;76(8):3622-6. doi: 10.1073/pnas.76.8.3622.
Freshly isolated sarcoplasmic reticulum vesicles contain 0.05 mol of tightly bound ADP and 0.03 mol of tightly bound ATP per mol of Ca2+, Mg2+-ATPase (ATP phosphohydrolase, EC 3.6.1.3). These values were increased to 0.1-0.2 mol ADP and 0.2-0.3 mol ATP per mol of ATPase after incubation of vesicles in the presence of MgATP and Ca2+ at 25 degrees C and pH 7.0. Half-maximal enrichment of tightly bound nucleotides was obtained with 2.5 mM ATP and 0.32 microM free Ca2+. Uncoupling of calcium transport from ATPase activity by mild acidic conditions or with ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid at pH 7.0 decreased the ability of the membranes to be enriched with tightly bound nucleotides and also decreased the content of tightly bound nucleotides of previously enriched membranes. Tightly bound [3H]nucleotides could only be partially displaced by reincubation under enrichment conditions. Tightly bound nucleotides are associated with energized calcium translocation but do not appear to be directly involved in the catalytic cycle.
新鲜分离的肌浆网囊泡，每摩尔Ca2 +、Mg2 + -ATP酶（ATP磷酸水解酶，EC 3.6.1.3）含有0.05摩尔紧密结合的ADP和0.03摩尔紧密结合的ATP。在25℃和pH 7.0条件下，囊泡在MgATP和Ca2 +存在下孵育后，这些值增加到每摩尔ATP酶0.1 - 0.2摩尔ADP和0.2 - 0.3摩尔ATP。用2.5 mM ATP和0.32 microM游离Ca2 +可获得紧密结合核苷酸的半最大富集量。在温和酸性条件下或在pH 7.0时用乙二醇双（β-氨基乙醚）-N，N，N'，N'-四乙酸使钙转运与ATP酶活性解偶联，降低了膜富集紧密结合核苷酸的能力，也降低了先前富集膜中紧密结合核苷酸的含量。在富集条件下再孵育只能部分取代紧密结合的[3H]核苷酸。紧密结合的核苷酸与活跃的钙转运相关，但似乎不直接参与催化循环。
