Effects of ATP on the interaction of Ca++, Mg++, and K+ with fragmented sarcoplasmic reticulum isolated from rabbit skeletal muscle.
Effects of ATP on the interaction of Ca++, Mg++, and K+ with fragmented sarcoplasmic reticulum isolated from rabbit skeletal muscle.
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DOI：
10.1085/jgp.50.5.1327
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发表时间：
1967-05
期刊：
影响因子：
--
通讯作者：
Leo B
中科院分区：
文献类型：
--
作者：
Carvalho AP;Leo B
从家兔骨骼肌中分离的肌浆网碎片在中性pH下的阳离子结合能力约为350 µeq/g蛋白质。相同的结合位点结合Ca、Mg、K和H离子，因此，ATP诱导的Ca选择性结合释放出与所吸收的Ca相当的其他阳离子。在pH值低于6.2时，越来越多的结合位点与H+相关，ATP诱导Ca主要交换为H+。在pH值高于6.2时，结合位点以Mg和K的形式存在，并且Ca被结合以交换这些阳离子。以每克蛋白质结合的阳离子的微当量表示的总结合Ca + Mg + K在各种pCa值下近似恒定，这表明Ca与其他阳离子的化学计量交换。为了实现相同程度的Ca与其他结合阳离子的交换，在不存在ATP的情况下，培养基中需要的游离Ca++浓度比在存在ATP的情况下所需的浓度高约1000倍。我们无法区分一种机制，即钙主动运输到一个区室的微粒体囊泡也含有结合位点是被动结合到这些网站交换镁，钾，和H和另一种ATP选择性增加的亲和力表面结合位点的钙。无论积累的机制，保留的钙并不有助于阳离子在膜部分的活动。咖啡因（10 mM）对Ca的结合没有影响，但释放出更不稳定的Ca部分，推测其积累超过结合的Ca。普罗维汀（5 mM）拮抗咖啡因的作用。乙酰胆碱和肾上腺素对Ca ~（2+）的结合无影响。
Fragmented sarcoplasmic reticulum isolated from skeletal muscle of the rabbit has a cation-binding capacity of about 350 µeq/g of protein at neutral pH. The same binding sites bind Ca, Mg, K, and H ions and, consequently, the selective binding of Ca induced by ATP releases an amount of the other cations equivalent to the Ca taken up. At pH values below 6.2, an increasing number of binding sites are associated with H+, and ATP induces exchange of Ca mostly for H+. At pH values above 6.2, the binding sites exist in the form of Mg and K, and Ca is bound in exchange for these cations. The total bound Ca + Mg + K, expressed in microequivalents of cations bound per gram of protein, is approximately constant at various pCa values, which indicates a stoichiometric exchange of Ca for the other cations. To accomplish the same degree of exchange of Ca for other cations bound, in the absence of ATP, concentrations of free Ca++ of about 1000-fold higher than those needed in the presence of ATP are required in the medium. We cannot distinguish between a mechanism whereby Ca actively transported into a compartment of the microsomal vesicles containing also the binding sites is bound passively to these sites in exchange for Mg, K, and H and another in which ATP selectively increases the affinity of surface-binding sites for Ca. Irrespective of the mechanism of accumulation, the Ca retained does not contribute to the activity of the cation in the membrane fraction. Caffeine (10 mM) has no effect on the binding of Ca, but releases a more labile fraction of Ca, which presumably accumulates in excess of the bound Ca. Procaine (5 mM) antagonizes the effect of caffeine. Acetylcholine and epinephrine have no effect on the binding of Ca.