Carafoli E, Zurini M, Benaim G
Ciba Found Symp. 1986;122:58-72. doi: 10.1002/9780470513347.ch5.
The calcium pump of plasma membranes is an ATPase of the E1E2 type; that is, it forms a phosphoenzyme during the reaction cycle and is inhibited by vanadate. It differs from the Ca2+-transporting ATPase of sarcoplasmic reticulum in molecular mass, immunological properties and Ca2+/ATP stoichiometry. Its affinity for calcium, which is low in the absence of calmodulin (Km, 10-20 microM), is increased by the latter (to a Km of about 0.5 microM). The effect of calmodulin is mimicked by acidic phospholipids (including the phosphorylated products of phosphatidylinositol), long-chain polyunsaturated fatty acids, and controlled treatment with a number of proteases. The ATPase has been purified to homogeneity from a number of plasma membranes using calmodulin affinity chromatography. The purified enzyme (a single polypeptide of molecular mass 138 kDa) pumps calcium into reconstituted liposomes in exchange for protons. Controlled trypsin proteolysis has shown that about one-third of the enzyme mass can be removed without impairing calcium transport. It has also indicated that the ability to bind calmodulin and to respond to it resides in a 9 kDa sequence of the enzyme molecule. The sequence contains a 4 kDa domain that binds calmodulin, and a 5 kDa domain which is essential for the stimulation.
质膜钙泵是一种E1E2型ATP酶；也就是说，它在反应循环中形成磷酸酶，并受钒酸盐抑制。它在分子量、免疫学特性和Ca2+/ATP化学计量方面与肌浆网的Ca2+转运ATP酶不同。在没有钙调蛋白的情况下，它对钙的亲和力较低（Km为10 - 20微摩尔），而钙调蛋白可增加其对钙的亲和力（至约0.5微摩尔的Km）。酸性磷脂（包括磷脂酰肌醇的磷酸化产物）、长链多不饱和脂肪酸以及用多种蛋白酶进行的可控处理可模拟钙调蛋白的作用。已使用钙调蛋白亲和层析从多种质膜中将ATP酶纯化至同质。纯化后的酶（一种分子量为138 kDa的单一多肽）将钙泵入重构脂质体以交换质子。可控的胰蛋白酶蛋白水解表明，去除约三分之一的酶量不会损害钙转运。这也表明，结合钙调蛋白并对其作出反应的能力存在于酶分子的一个9 kDa序列中。该序列包含一个结合钙调蛋白的4 kDa结构域和一个对刺激至关重要的5 kDa结构域。
