兔肝金属硫蛋白结合铅离子的圆二色性光谱研究

从锌诱导的家兔肝脏中分离纯化得到金属硫蛋白两种亚型：ＺｎＭＴ－Ⅰ和ＺｎＭＴ－Ⅱ．在酸性条件下脱金属，经Ｓｅｐｈａｄｅｘ Ｇ－２５柱层析得到脱金属硫蛋白（ａｐｏＭＴｓ）．用圆二色性（ＣＤ）光谱法研究，发现两种亚型ａｐｏＭＴｓ 与Ｐｂ２＋ 的结合依赖于Ｐｂ２＋ 的加入比例及ｐＨ 值．ａｐｏＭＴ－Ⅰ在ｐＨ３～５之间，ａｐｏＭＴ－Ⅱ在ｐＨ４～６之间与Ｐｂ２＋ 结合形成特征簇合物Ｐｂ７ＭＴｓ，其ＣＤ谱图特征峰位于３１６ｎｍ （－ ），２７０ ｎｍ （＋ ），２４５ ｎｍ （＋ ）及２２５ ｎｍ （－ ），提示解铅中毒的最佳条件应控制在弱酸性环境．不同亚型ａｐｏＭＴｓ 与Ｐｂ２＋ 的结合方式各不相同：Ｐｂ２＋ 与ａｐｏＭＴ－Ⅰ的结合采取平均分配的方式，而与ａｐｏＭＴ－Ⅱ则为选择性结合方式，表明这两种亚型在解铅毒功能上存在差异．

Study on Rabbit Liver Metallothioeins Binding with Lead Ion by Circular Dichroism

Two isoforms of metallothioneins ZnMT Ⅰ and ZnMT Ⅱ were prepared from the rabbit liver induced by zinc.They were demetalled in acidic condition,then applied Sephadex G 25 to gain apoMTs free of metals.By using Circular Dichroism(CD)spectroscopy method,Pb 2+ binding to rabbit liver apoMTs was found to depend on the Pb 2+ ∶MT stoichiometric ratios and pH.The optimum pH of apoMTs with other metals was 7.0;in contrast,the characteristic structure Pb 7MTs were formed:apoMT Ⅰ with Pb 2+ at pH 3～5(the optimum pH was 3.5),apoMT Ⅱ with Pb 2+ at pH 4～6(the optimum pH value was 4.5),whose characteristic CD bands showed at 316 nm(-),270 nm(+),245 nm(+)and 225 nm(-),suggesting that the optimum conditions of lead detoxification should be controlled at low pH value.Two isoforms adopted different binding ways,the way of apoMT Ⅰ with Pb 2+ was random;however,the way of apoMT Ⅱ with Pb 2+ was selective,which means Pb 2+ bound to apoMT Ⅱ in order to form one domain first,suggesting that two isoforms might be different in lead detoxification properties.