With the aim of extending our knowledge on the reaction pathways of Zn-metallothionein (MT) and apo-MT species in the presence of Hg(II), we monitored the titration of Zn7-MT, Zn4 -aMT and Zn3 -bMT proteins, at pH 7 and 3, with either HgCl2or Hg(ClO4 )2 by CD and UV-vis spectr-oscopy. Detailed analysis of the optical data revealed that standard variables, such as the pH of the solution, the binding ability of the counter-ion (chloride or perchlorate), and the time elapsedbetween subsequent additions ofHg(II) to the protein, play a determinant role in the stoichiometry, stereochemistry anddegree of folding of theHg-MT species. Despite the fact that the effect of these variables is unques-tionable, it is difficult to.
