Metallothionein-like protein in the least killifish Heterandria formosa and its role in cadmium resistance.

Metallothioneins (MTs) are a class of low molecular weight, cysteine-rich, metal-binding proteins ubiquitous in animals. They function in metal regulation and detoxification. An MT-like protein was separated by gel-permeation high-performance liquid chromatography (HPLC) in the least killifish Heterandria formosa exposed to 6 mg/L of Cd for 26 h. Western blot analysis showed that this protein cross-reacted with a cod-MT antibody. We quantified MT-like protein levels by the Cd-hemoglobin saturation assay in fish from two Cd-resistant and two control laboratory populations. Fish from the resistant populations had higher MT-like protein levels than those from the control populations; this difference was found for basal levels and for levels after 26 h of exposure to Cd. Our results suggest that the MT-like protein detoxified Cd in the least killifish and accounted for at least part of the increased resistance in the Cd-resistant laboratory populations.