Caldwell C C, Hornyak S C, Pendleton E, Campbell D, Knowles A F
Department of Chemistry, San Diego State University, California 92182-1030, USA.
Arch Biochem Biophys. 2001 Mar 1;387(1):107-16. doi: 10.1006/abbi.2000.2216.
The major ectonucleoside triphosphate phosphohydrolase in the chicken gizzard smooth muscle membranes is an ecto-ATPase, an integral membrane glycoprotein belonging to the E-ATPase (or E-NTPDase) family. The gizzard ecto-ATPase is distinguished by its unusual kinetic properties, temperature dependence, and response to a variety of modulators. Compounds that promote oligomerization of the enzyme protein, i.e., concanavalin A, chemical cross-linking agent, and eosin iodoacetamide, increase its activity. Compounds that inhibit some ion-motive ATPases, e.g., sulfhydryl reagents, xanthene derivatives, NBD-halides, and suramin, also inhibit the gizzard ecto-ATPase, but not another E-ATPase, the chicken liver ecto-ATP-diphosphohydrolase, which contains the same conserved regions as the ecto-ATPase. Furthermore, inhibition of the gizzard ecto-ATPase by these compounds as well as detergents is not prevented by preincubation of the membranes with the substrate, ATP, indicating that their interaction with the enzyme occurs at a locus other than the catalytic site. On the other hand, the inhibitory effect of these compounds, except suramin, is abolished or reduced if the membranes are preincubated with concanavalin A. It is concluded that these structurally unrelated modulators exert their effect by interfering with the oligomerization of the ecto-ATPase protein. Our findings suggest that, under physiological conditions, the gizzard smooth muscle ecto-ATPase may exhibit a range of activities determined by membrane events that affect the status of oligomerization of the enzyme.
鸡砂囊平滑肌膜中的主要胞外核苷三磷酸磷酸水解酶是一种胞外ATP酶，它是一种属于E - ATP酶（或E - NTPDase）家族的整合膜糖蛋白。鸡砂囊胞外ATP酶以其异常的动力学特性、温度依赖性以及对多种调节剂的反应而著称。促进酶蛋白寡聚化的化合物，即伴刀豆球蛋白A、化学交联剂和曙红碘乙酰胺，会增加其活性。抑制某些离子驱动ATP酶的化合物，如巯基试剂、呫吨衍生物、NBD - 卤化物和苏拉明，也会抑制鸡砂囊胞外ATP酶，但不会抑制另一种E - ATP酶，即鸡肝胞外ATP二磷酸水解酶，后者与胞外ATP酶含有相同的保守区域。此外，用底物ATP对膜进行预孵育并不能阻止这些化合物以及去污剂对鸡砂囊胞外ATP酶的抑制作用，这表明它们与酶的相互作用发生在催化位点以外的部位。另一方面，如果膜用伴刀豆球蛋白A进行预孵育，这些化合物（除苏拉明外）的抑制作用会被消除或减弱。得出的结论是，这些结构不相关的调节剂通过干扰胞外ATP酶蛋白的寡聚化发挥作用。我们的研究结果表明，在生理条件下，鸡砂囊平滑肌胞外ATP酶可能表现出一系列由影响酶寡聚化状态的膜事件所决定的活性。
