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.
Key words
Metallothioneins /
Lead ion /
CD
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