Edwards R A, Trainer V L, Baden D G
University of Miami, Rosenstiel School of Marine and Atmospheric Science, NIEHS Marine and Freshwater Biomedical Sciences Center, FL 33149.
Brain Res Mol Brain Res. 1992 Jun;14(1-2):64-70. doi: 10.1016/0169-328x(92)90011-y.
The brevetoxins (PbTx series), neurotoxins produced by the marine dinoflagellate Ptychodiscus brevis, cause dose-dependent activation of the voltage-sensitive sodium channel (VSSC). Saturation binding studies employing adult rat brain synaptosomes suggest the existence of a high affinity/low capacity (HA/LC) and a second, lower affinity/higher capacity (LA/HC) class of binding site. LIGAND analysis of saxitoxin and brevetoxin saturation binding data yields a statistically identical Bmax for the brevetoxin high affinity/low capacity (HA/LC) site (1.9 +/- 0.98 pmol/mg protein) and for saxitoxin (1.72 +/- 0.78 pmol/mg protein; P less than 0.001). The stoichiometry of HA/LC brevetoxin binding and saxitoxin binding approaches 1:1. Covalent modification of synaptosomes with a brevetoxin photoaffinity probe preferentially blocks the HA/LC binding site. Hill plots of saturation binding data yield a coefficient of 1.0 +/- 0.02, demonstrating a lack of cooperativity between brevetoxin binding site classes. Kd and Bmax for toxin binding are independent of membrane polarity, intimating that the observed low affinity/high capacity (LA/HC) binding characteristics are not due to modification of the HA/LC site, and strongly argue for the presence of multiple brevetoxin binding site classes. Half-maximal binding at the LA/HC site, and strongly argue for the presence of multiple brevetoxin binding site classes. Half-maximal binding at the LA/HC site occurs at concentration ranges for which the brevetoxins allosterically modulate binding of other natural toxins to their specific sites.
短裸甲藻毒素（PbTx系列）是由海洋双鞭毛藻短裸甲藻产生的神经毒素，可引起电压敏感性钠通道（VSSC）的剂量依赖性激活。采用成年大鼠脑突触体的饱和结合研究表明存在一类高亲和力/低容量（HA/LC）结合位点以及第二类亲和力较低/容量较高（LA/HC）的结合位点。对石房蛤毒素和短裸甲藻毒素饱和结合数据进行LIGAND分析，结果显示短裸甲藻毒素高亲和力/低容量（HA/LC）位点的最大结合量（Bmax）（1.9±0.98 pmol/mg蛋白质）与石房蛤毒素的最大结合量（1.72±0.78 pmol/mg蛋白质；P<0.001）在统计学上相同。HA/LC短裸甲藻毒素结合与石房蛤毒素结合的化学计量比接近1:1。用短裸甲藻毒素光亲和探针共价修饰突触体可优先阻断HA/LC结合位点。饱和结合数据的希尔图得出系数为1.0±0.02，表明短裸甲藻毒素结合位点类别之间缺乏协同性。毒素结合的解离常数（Kd）和最大结合量（Bmax）与膜极性无关，这表明观察到的低亲和力/高容量（LA/HC）结合特征并非由于HA/LC位点的修饰，有力地证明了存在多种短裸甲藻毒素结合位点类别。LA/HC位点的半数最大结合发生在短裸甲藻毒素变构调节其他天然毒素与其特定位点结合的浓度范围内。
