The circular dichroism was used to study the complexation of two isoforms of rabbit liver apo-metallothioneins (apo-MT1 and apo-MT2) with Cd
2+ ion and the influence of Cd
2+ ion on the conformation of reconstituted MTs. The stability of sulfhydryls of apo-MT has been investigated at the room temperature in the presence of air. The reconstitutions of apo-MT1 with Cd
2+ ion were carried out at
pH 4.71 (stable state) and
pH 7.9 (with 90% sulfhydryls oxidated) respectively. it was found that the characteristic CD band at 257 nm(+), 238 nm(?), 226 nm(+) of reconstituted MT with Cd
2+ ion was the same as native MT at
pH 4.71, however only one peak at 243 nm(+) appeared on the CD spectra at
pH 7.9 which arose from mononuclear complexes with four separated thiolate ligands per Cd
2+ ion. The CD spectra of apo-MTs+7 eq Cd
2+ system were measured at various
pH values. It was found that the peak at 256 nm of apo-MT1 binding Cd
2+ ion split into two small peaks at
pH between 2.42 and 3.02, and became one peak at
pH 3.32, while the shapes of Cd peaks of apo-MT2 binding Cd
2+ ion did not change with
pH, indicating that the binding sites and pathway of apo-MT1 binding Cd
2+ ion were different from those of apo-MT2. A possible mechanism was suggested.
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