Study of complexing properties of the alpha and beta metallothionein domains with cadmium and/or zinc using electrospray ionisation mass spectrometry

A study of the complexing properties of the alpha and beta metallothionein domains with cadmium and/or zinc was performed, at pH 8, using electrospray ionisation mass spectrometry (ESI-MS). The applied method allows one to de termine the molecular mass, and hence, the stoichiometry of compounds at di fferent proportions of metal ions to the alpha and beta domains. The alpha and beta domains are capable of complexing cadmium and/or zinc, separately or after simultaneous or sequential additions of metal ions in the ratios a lpha :M = 1:4 and beta :M = 1:3. In the case of binary mixtures, alpha or b eta + Cd or Zn pure complexes are formed: Cd(2)alpha, Cd(4)alpha and Cd(5)a lpha, Zn(3)alpha and Zn(4)alpha for the a domain and Cd(3)beta and Cd(4)bet a, Zn(3)beta for beta domain, whereas in the case of tertiary mixtures alph a or beta + [Cd + Zn], mixed cadmium and zinc complexes prevail: Cd(3)Zn(1) alpha, Cd(2)Zn(2)alpha, Cd(1)Zn(3)alpha and Cd(2)Zn(1)beta and Cd(1)Zn(2)be ta. These mixed complexes co-exist with pure cadmium complexes Cd(4)alpha a nd Cd(4)beta and Cd(3)beta in an excess of metal ions, particularly cadmium . So several stable forms of complexation of cadmium and zinc with the alph a and beta domains exist, depending on the composition of the solution. Whe n one of the cations is added to a solution containing the alpha or beta do main complexed with the other cation, it is incorporated into the molecule resulting in its reorganisation. which is illustrated by changes in the abu ndance of pure and mixed complexes. (C) 2001 Elsevier Science B.V. All righ ts reserved.