笋瓜籽毒蛋白Maximin──一种新的蛋白质生物合成抑制剂的分离纯化及性质

Maximin──A New Inhibitory Protein of Protein Synthesis:Purification and Properties

笋瓜（Ｃｕｃｕｒｂｉｔａｍａｘｉｍａ）种籽经去壳捣碎，乙醚脱脂，硫酸铵分级沉淀，阳离子交换层析及凝胶过滤等步骤，纯化到一种有蛋白质生物合成抑制活性的碱性蛋白，命名为Ｍａｘｉｍｉｎ，ＳＤＳ－ＰＡＧＥ显示单一条带，其分子量约为２８ｋＤ。该蛋白对兔网织红细胞裂解液的蛋白生物合成有较强的抑制，ＩＣ_（５０）为４．０×１０^（－１０）ｍｏｌ／Ｌ，与天花粉蛋白（ＴＣＳ）毒性相似。从这些特性可见，该蛋白似为单链核糖体失活蛋白（ＲＩＰ）家族中的新成员，可望作为免疫毒素的一种新“弹头”。

A series of methods including ammonium sulfate precipitation, CM-52 ion-exchange chromatography,Sephacryl S-100 gel filtration and HPLC were applied to isolate maximin from the seeds of Cucurbita maxima. The results of SDS-PAGE and HPLC gel filtration indicated that its molecular weight was around 28kD. Inhibition to protein synthesis was primarily determined by the cell free system of rabbit reticulocyte lysate which displayed that the IC(50) of maximin was at the same level of that of TCS. The statistics discussed in this paper implied maximin is likely to be a new member of RIPs and becomes a novel toxic moiety of immunotoxin.