Copper replacement of cadmium-binding alpha-fragment of metallothionein expressed in Escherichia coli.

Titration studies of Cd-binding alpha-fragment, the carboxyl-terminal half of human metallothionein-2, which was independently expressed in Escherichia coli as a Cd-binding form, with Cu were performed. The Cu saturated alpha-fragment was not obtained when the alpha-fragment incubated with Cu (I), although completely saturated MT with Cu (I) was successfully obtained in the same conditions. The stoichiometry of the alpha-fragment replaced with Cu (I) was Cu 4 and Cd 1. It is considered that the Cu-binding alpha-fragment required the presence of Cd (II) to form a stable structure. Our results could suggest that each fragment was independent in the metal binding processes, e.g. alpha-fragment for Cd-binding.