Metallotioneins as indicators of trace metal pollution

Metallothioneins (MTs) are low-molecular-weight cystein-rich metal-binding proteins that are involved in detoxification and homeostasis of heavy metals. The ubiquitous distribution of MTs in virtually all types of organisms studied to date attests to the conserved nature of MTs and their function. The biological function of MTs is likely related to the physiologically relevant metals that these proteins bind. In mammals, MT is found to bind zinc and copper under normal physiological conditions.Both zinc and copper are trace metals that are essential for life. Recent studies have produced strong evidence to support the idea that MT functions as a metal chaperone for the regulation of gene expression and for synthesis and functional activity of proteins, such as metalloproteins and metal-dependent transcription factors. MT could thus serve as a reservoir of essential metals. MTs are inducible proteins. Exposure of the organisms to high levels of heavy metals (e.g. Zn, Cu, Cd, and Hg) and the following increase of heavy metal cations in the cells stimulates metalloprotein neosynthesis. The importance of metallothionein (MT) in toxicologic responses to heavy metals was early recognized for potential application as “biomarker” of organism exposure to heavy metals in aquatic environments.