Gatto Craig, Helms Jeff B, Prasse Megan C, Huang Sheng-You, Zou Xiaoqin, Arnett Krista L, Milanick Mark A
Division of Biomedical Sciences, Department of Biological Sciences, Illinois State University, Normal, Illinois 61790-4120, USA.
Biochemistry. 2006 Nov 7;45(44):13331-45. doi: 10.1021/bi060667j.
The effects of three classes of organic cations on the inhibition of the plasma membrane Ca pump (PMCA) were determined and compared to inhibition of the Na pump. Quaternary amines (tetramethylammonium, tetraethylammonium, and tetrapropylammonium, TMA, TEA, and TPA, respectively) did not inhibit PMCA. This is not to imply that PMCA is inherently selective against monovalent cations because guanidine and tetramethylguanidine inhibited PMCA by competing with Ca(2+). The divalent organic cation, ethyl diamine, inhibited PMCA but was not competitive with Ca(2+). In contrast, propyl diamine did compete with Ca(2+) and was about 10-fold more potent than butyl diamine in inhibiting PMCA. For the Na pump, both TEA and TPA inhibited, but TMA did not. TEA, guanidine, and tetramethylguanidine inhibition was competitive with Na(+) for ATPase activation and with K(+) for pNPPase activation, both of which are cytoplasmic substrate cation effects. Thus, these findings are consistent with TEA, guanidine, and tetramethylguanidine inhibiting from the cytoplasmic side of the Na pump; in contrast, we have previously shown that TPA did not inhibit from the cytoplasmic side. The divalent alkane diamines ethyl, propyl, and butyl diamine all inhibited the Na pump and all competed at the intracellular surface. The order of potency was ED > PD > BD consistent with an optimal size for binding; similarly, for the quaternary amines TMA is apparently too small to make appropriate contacts, and TPA is too large. Homology models based upon the high-resolution SERCA structure are included to contextualize the kinetic observations.
测定了三类有机阳离子对质膜钙泵（PMCA）的抑制作用，并与对钠泵的抑制作用进行了比较。季铵盐（分别为四甲基铵、四乙基铵和四丙基铵，即TMA、TEA和TPA）不抑制PMCA。这并不意味着PMCA对单价阳离子具有内在选择性，因为胍和四甲基胍通过与Ca(2+)竞争来抑制PMCA。二价有机阳离子乙二胺抑制PMCA，但不与Ca(2+)竞争。相比之下，丙二胺确实与Ca(2+)竞争，并且在抑制PMCA方面比丁二胺强约10倍。对于钠泵，TEA和TPA都有抑制作用，但TMA没有。TEA、胍和四甲基胍的抑制作用在ATP酶激活方面与Na(+)竞争，在对硝基苯磷酸酶（pNPPase）激活方面与K(+)竞争，这两者都是细胞质底物阳离子效应。因此，这些发现与TEA、胍和四甲基胍从钠泵的细胞质侧进行抑制是一致的；相比之下，我们之前已经表明TPA不是从细胞质侧进行抑制的。二价链烷二胺乙二胺、丙二胺和丁二胺都抑制钠泵，并且都在细胞内表面进行竞争。效力顺序为ED＞PD＞BD，这与结合的最佳大小一致；同样，对于季铵盐，TMA显然太小而无法进行适当接触，而TPA又太大。基于高分辨率肌浆网钙ATP酶（SERCA）结构的同源模型被纳入以解释动力学观察结果。
