TMVI 在天竺鼠神經鍵體上之專一性結合

Abstract

TMVI是由龜殼花毒液純化得來的蛋白質，具有磷脂?A2活性，其分子量約為16,000。本文利用125I標示後的TMVI測出它在天竺鼠神經鍵體上的高親合力專一性結合。由數學作圖所求得的解離常數(Kd）為3.7×10-7M，而未碘化之TMVI抑制125I-TMVI結合之IC50則為5×10-8 M。很明顯地，碘化過程降低TMVI對天竺鼠神經鍵體細胞膜之親合力。碘化也會使TMVI的磷脂?A2活性下降45％。125I-TMVI在天竺鼠神經鍵體上之最大結合量（Bmax）為19.6 pmole/mg of protein。 以protease K或胰蛋白?處理天竺鼠神經鍵體，並不能影響125I-TMVI在天竺鼠神經鍵體上之結合，因此，結合體可能並非蛋白質。而以Sr2+離子取代Ca2+離子，125I-TMVI仍有結合能力，因此125I-TMVI在天竺鼠神經鍵體上的專一性結合並不需要PLA2活性。某些其他PLA2也能抑制125I-TMVI在天竺鼠神經鍵體上的專一性結合，惟其抑制能力不一。

TMVI, a PLA2 with molecular weight of 16,000 was purified from Trimeresurus mucrosquamatus venom. TMVI was radioactively iodinated and used to demonstrate specific binding to synaptosomes. The dissociation constant (Kd) calculated from the double-reciprocal plot of the binding curve is 3.7*10-7M. For comparision, unlabeled TMVI inhibited the binding of 125I-TMVI with an IC50 of 5*10-8M. Obviously, iodination of TMVI affect the protein to some degree. The iodination also caused 45% decrease in the PLA2 activity of TMVI. The number of binding sites in the synaptosome is 19.6 pmole/mg of protein. Because the binding activity of 125I-TMVI to synaptosomes is resistant to proteolysis, the binding site may be other than proteins. Competition experiments showed that several other PLA2 variants can displace 125I-TMVI binding with the different ability.