The Cd-Chelex assay: a new sensitive method to determine metallothionein containing zinc and cadmium

A rapid and sensitive one-vial procedure to determine metallothionein (MT) containing zinc (Zn) and cadmium (Cd) is described. New features of this Cd-saturation method are: high molecular weight Cd-binding proteins are denatured by treatment with acetonitrile (50% final concentration), and excess of Cd is bound to a cation exchange resin (Chelex-100). With this method, MT has been measured, e.g. in liver of control and zinc- or cadmium-treated rats, in human liver and in cultured human fibroblasts down to absolute amounts of 0.1 microgram. The Cd-Chelex assay is 10 times more sensitive than the established Cd-heme assay (Dieter et al. 1986) and therefore is particularly suitable to quantify MT in small tissue samples (e.g., liver biopsies of a few milligrams) and in extrahepatic tissues or cell cultures with low MT concentrations.