Gold replacement of cadmium, zinc-binding metallothionein.

We analyzed the gold-binding capacity and property of metallothionein by replacement of the Cd, Zn-binding metallothionein with Au. Unlike native Cd,Zn-metallothionein, the ultraviolet absorption spectrum of Au-metallothionein was very similar to that of apo-metallothionein. The maximum binding ratios of Au and Cd per metallothionein replaced with Au were 9 and 2, respectively. Since the maximum binding ratio of Au per metallothionein with Au (III) was estimated to be 12 g atoms of Au per metallothionein, it was inferred that Au was bound to metallothionein as Au (I). The results indicate that Au (III) exhibits stronger binding affinity than Zn and Cd to metallothionein.