摘要
心臟毒素( CTX )為台灣眼鏡蛇Naja atra蛇毒主要的成分，具有溶血、使神經及肌肉細胞去極化、干擾細胞離子通道平衡以及細胞毒性等特性。當生物體被毒蛇咬傷，被咬部位產生發炎腫脹，進而造成個體死亡，免疫系統是身體防禦的第一線，其中嗜中性白血球具有快速移動到感染部位抵抗病菌的特性，基於此針對心臟毒素是否可調節免疫細胞的功能加以研究，我們發現心臟毒素對嗜中性白血球具有明顯的毒性，並發現心臟毒素A2在不使細胞崩解(lysis)的濃度下會引起嗜中性白血球細胞內的鈣離子濃度增加，此增加的幅度和心臟毒素的濃度成正比，而且和胞外鈣離子的存在與否無關，而細胞內鈣離子濃度的增加通常為細胞死亡的特徵之一，在不造成細胞崩解的情況下，研究心臟毒素所引起細胞內鈣離子濃度增加的機制。就目前已知的細胞內鈣離子訊號傳遞途徑來看，發現心臟毒素A2引起效應和已知的途徑無關，故推測和細胞膜的作用有關。另一方面，從A2的結構來探討，心臟毒素A2及A4兩者只有N端第一個氨基酸序列的差異，CTX A2的N端第一個氨基酸為Leucine (Leu1)。在細胞毒性的比較上，心臟毒素A4的毒性遠大於心臟毒素A2，但是A4並不會引起細胞內鈣離子濃度的增加，因此利用化學修飾法將心臟毒素A2作N端修飾，來探討是否因為N端的差異造成細胞內鈣離子濃度的改變。我們發現去除N端Leu1的CTX A2不會引起細胞內部鈣離子濃度的增加。因此證明了CTX A2的N端第一個氨基酸在調節細胞內部鈣離子的功能上扮演關鍵的角色。

Abstract
Cardiotoxins (CTXs) are the major component in the venom of Naja atra. They cause hemolysis, depolarization of cardiac muscle cells, and contraction of skeletal muscle. They also interrupt of the equilibrium of the ion channels, and exhibit various cytotoxicity effects. When one is bitten by a snake, the wound will induce inflammation and swelling,which will eventually lead to death. The immune system, including leukocytes and lymphocytes, is the most important defense mechanism in the human body. Among these different cells, neutrophils can migrate rapidly to the infected regions and kill the pathogens.In this work, we study the effects of CTX to the dosage of calcium of neutrophils. We found that CTX A2 can induce intracellular increase of calcium but not to the level that would cause the death of the cells. This increase is dependent on the dosage of CTX A2 but independent from extracellular dosage of calcium. We discover that CTX A2 has nothing to do with known signal transduction pathway. As a result, we infer this effect bears directly on the interaction between CTX A2 and the cell membrane. Comparing CTX A2 and CTX A4, we find that there is the only one structural difference in the first N-terminal amino acid sequence.

The first N-terminal amino acid sequence of CTX A2 is Leu. In the view of cytotoxicity, CTX A4 is more toxic than CTX A2. But CTX A4 does not induce intracellular calcium increase in the real time calcium experiment. Therefore, modifying the N-terminal amino acid sequence of CTX A2 may clarify whether the N-terminal amino acid sequence is a possible factor to cause the intracellular calcium increase. We find that the deleted N-terminal Leu1 of CTX A2 dos not induce intracellular calcium increase. Thus we proved that the Leu1 of CTX A2 is the most crucial factor for intracellular calcium increase.

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