Paucek Petr, Jabůrek Martin
Department of Biology, Portland State University, Portland, Oregon 97207, USA.
Biochim Biophys Acta. 2004 Nov 4;1659(1):83-91. doi: 10.1016/j.bbabio.2004.03.019.
The Na(+)/Ca(2+) antiporter was purified from beef heart mitochondria and reconstituted into liposomes containing fluorescent probes selective for Na(+) or Ca(2+). Na(+)/Ca(2+) exchange was strongly inhibited at alkaline pH, a property that is relevant to rapid Ca(2+) oscillations in mitochondria. The effect of pH was mediated entirely via an effect on the K(m) for Ca(2+). When present on the same side as Ca(2+), K(+) activated exchange by lowering the K(m) for Ca(2+) from 2 to 0.9 microM. The K(m) for Na(+) was 8 mM. In the absence of Ca(2+), the exchanger catalyzed high rates of Na(+)/Li(+) and Na(+)/K(+) exchange. Diltiazem and tetraphenylphosphonium cation inhibited both Na(+)/Ca(2+) and Na(+)/K(+) exchange with IC(50) values of 10 and 0.6 microM, respectively. The V(max) for Na(+)/Ca(2+) exchange was increased about fourfold by bovine serum albumin, an effect that may reflect unmasking of an autoregulatory domain in the carrier protein.
钠钙反向转运体从牛心线粒体中纯化出来，并重组到含有对钠或钙具有选择性的荧光探针的脂质体中。钠钙交换在碱性pH下受到强烈抑制，这一特性与线粒体中快速的钙振荡有关。pH的影响完全是通过对钙的米氏常数（Km）的作用来介导的。当钾与钙在同一侧时，钾通过将钙的Km从2微摩尔降低到0.9微摩尔来激活交换。钠的Km为8毫摩尔。在没有钙的情况下，该转运体催化高速度的钠锂和钠钾交换。地尔硫䓬和四苯基鏻阳离子分别以10和0.6微摩尔的半数抑制浓度（IC50）抑制钠钙和钠钾交换。牛血清白蛋白使钠钙交换的最大反应速度（Vmax）增加了约四倍，这种作用可能反映了载体蛋白中一个自调节结构域的暴露。
