金属硫蛋白结合铅离子的竞争反应和置换反应研究

Study on Competition Reaction and Replacement Reaction of Metallothioneins with Lead Ion

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 :Zn2 Cd5MT Ⅰ和Zn2 Cd5MT 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Zn2 Cd5MTs中的Zn2 + ,且其置换行为也存在着亚型上的差异。提示Zn2 Cd5MT Ⅱ可能有效地解铅中毒。

Two isoforms metallothioneins:Zn\-7MT Ⅰ and Zn\-7MT 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, Zn\-2Cd\-5MT\|Ⅰ and Zn\-2Cd\-5MT\|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 Zn\-7MT\|Ⅰ or in Zn\-7MT\|Ⅱ; on the contrary, lead ion can replace zinc ion both in Zn\-2Cd\-5MT Ⅰ and in Zn 2Cd 5MT Ⅱ; moreover, these two isoforms Zn 2Cd 5MTs display differences in replacement reaction. It suggests Zn 2Cd 5MT Ⅱ may detoxify lead effectively.