Chang C C, Su M J
Br J Pharmacol. 1981 Jun;73(2):495-503. doi: 10.1111/j.1476-5381.1981.tb10448.x.
1 Crotapotin, the acidic subunit of crotoxin, greatly potentiated the presynaptic effect of isolated basic phospholipase A (PLA) of crotoxin in both mouse diaphragm and chick biventer cervicis muscles whereas the myotoxic effect was not affected significantly.2 In contrast to crotoxin PLA, the presynaptic effects of notexin and notechis-5, self-active single chain toxins, were antagonized by crotapotin while actions of beta-bungarotoxin were not affected.3 By assaying PLA activity, crotoxin PLA was found to be unstable in physiological salt solution, especially when in contact with muscle, due to massive non-specific binding to and destruction by the muscle.4 The decline of crotoxin PLA was greatly reduced by the presence of crotapotin but not by another acidic protein, volvatoxin A(2), or heparin.5 Notechis-5 was found to be stable even when in the presence of muscles.6 [(3)H]-acetylated crotoxin PLA, which retained about 40% of its original enzyme and presynaptic blocking activities, also bound rapidly to the mouse diaphragm on incubation and this binding was greatly hindered by the simultaneous addition of crotapotin.7 The prevention of binding of crotoxin PLA by crotapotin occurred mostly at those sites where the binding was easily dissociable on washing. No antagonism of binding occurred at the firmly binding site.8 The binding of [(3)H]-acetylated crotapotin was much less than that of crotoxin PLA, and interestingly, the binding was increased by the latter, suggesting that crotapotin may be first bound to the diaphragm together with crotoxin PLA.9 No specific binding at the endplate zone was found either for crotoxin PLA or for crotapotin.10 It is concluded that crotapotin potentiates the presynaptic effect of crotoxin PLA by curtailing its non-specific affinity with muscles, minimizing its dispersal and destruction en route to the nerve terminal, but not by acting as an affinity probe for the nerve terminal.
响尾蛇毒素的酸性亚基巴曲亭，在小鼠膈肌和鸡二腹肌中，能显著增强分离出的响尾蛇毒素碱性磷脂酶A（PLA）的突触前效应，而对其肌毒性效应无显著影响。
与响尾蛇毒素PLA相反，自身具有活性的单链毒素——诺维毒素和五步蛇毒素5的突触前效应会被巴曲亭拮抗，而β - 银环蛇毒素的作用则不受影响。
通过检测PLA活性发现，响尾蛇毒素PLA在生理盐溶液中不稳定，尤其是与肌肉接触时，这是由于其与肌肉大量非特异性结合并被破坏。
巴曲亭的存在能大大减少响尾蛇毒素PLA的降解，但另一种酸性蛋白——芋螺毒素A（2）或肝素则不能。
发现五步蛇毒素5即使在有肌肉存在的情况下也很稳定。
[³H] - 乙酰化响尾蛇毒素PLA在保留约40%的原始酶活性和突触前阻断活性的情况下，在孵育时也能迅速与小鼠膈肌结合，同时加入巴曲亭会极大地阻碍这种结合。
巴曲亭对响尾蛇毒素PLA结合的阻止主要发生在那些洗涤时容易解离的结合位点。在牢固结合位点没有发生结合拮抗。
[³H] - 乙酰化巴曲亭的结合远少于响尾蛇毒素PLA，有趣的是，后者会增加其结合，这表明巴曲亭可能首先与响尾蛇毒素PLA一起结合到膈肌上。
在终板区未发现响尾蛇毒素PLA或巴曲亭有特异性结合。
得出结论：巴曲亭通过减少响尾蛇毒素PLA与肌肉的非特异性亲和力，使其在到达神经末梢途中的扩散和破坏最小化，从而增强其突触前效应，而不是通过作为神经末梢的亲和探针来起作用。
