Abstract: Two isoforms metallothioneins: Zn₇MT-Ⅰ and Zn₇MT-Ⅱ were prepared from the rabbit liver induced by zinc after isolation and purification. They were demetalled in acidic condition, then applied Sephadex G-25 to gain apoMTs free of metals. In a similar way, Zn₂Cd₅MT-Ⅰ and Zn₂Cd₅MT-Ⅱ were prepared from the rabbit liver induced by cadmium. By using Circular Dichroism (CD) spectroscopy method and Ultraviolet (UV) absorption spectrophotometry, competition reaction and replacement reaction of metallothioneins with lead ion were investigated. Competition reaction shows that ZnPbMT-Ⅰ is formed while lead ion and zinc ion bind competitively to apoMT-Ⅰ；however, apoMT-Ⅱ's metal binding sites are all took up by lead ion, which means apoMT-Ⅱ is more sensitive to lead ion than apoMT-Ⅰ. Replacement reaction shows that lead ion can't replace zinc ion either in Zn₇MT-Ⅰ or in Zn₇MT-Ⅱ; on the contrary, lead ion can replace zinc ion both in Zn₂Cd₅MT-Ⅰ and in Zn₂Cd₅MT-Ⅱ；moreover, these two isoforms Zn₂Cd₅MTs display differences in replacement reaction. It suggests Zn₂Cd₅MT-Ⅱ may detoxify lead effectively.

Key words: Metallothioneins, Lead Ion, Competition Reaction, Replacement Reaction, CD, UV

摘要： 从锌诱导的家兔肝脏中分离纯化得到两种亚型的金属硫蛋白(MTs)：Zn₇MT-Ⅰ和Zn₇MT-Ⅱ，在酸性条件下脱金属得脱金属硫蛋白(apoMTs)。从镉诱导的家兔肝脏中分离纯化得：Zn₂Cd₅MT-Ⅰ和Zn₂Cd₅MT-Ⅱ。采用圆二色性(CD)光谱法和紫外(UV)吸收光谱法研究金属硫蛋白结合铅离子的竞争反应和置换反应。竞争反应显示：Pb²⁺和Zn²⁺竞争结合apoMT-Ⅰ形成的是金属混配的金属硫蛋白；而apoMT-Ⅱ的金属结合位点则完全被Pb²⁺所占据，表明apoMT-Ⅱ对Pb²⁺更为敏感。置换反应显示：Pb²⁺既不能置换出Zn₇MT-Ⅰ中的Zn²⁺，也不能置换出Zn₇MT-Ⅱ中的Zn²⁺；但Pb²⁺能完全置换出Zn₂Cd₅MTs中的Zn²⁺，且其置换行为也存在着亚型上的差异。提示Zn₂Cd₅MT-Ⅱ可能有效地解铅中毒。

关键词: 金属硫蛋白, 铅离子, 竞争反应, 置换反应, 圆二色性光谱法, 紫外光谱法