Metallothioneins (MTs) in marine molluscs

The presence of MTs in marine molluscs was firstly hypothesized in oyster a nd in mussel during the seventies, however mussel's and oysters' MTs were c ompletely purified and sequenced rather later. Already from the first studi es it was evident that the purification of molluscan MTs was more difficult than in mammals. Mussel's MTs are characterized by the presence of a monom eric and a dimeric form. Several physiological and biochemical parameters c an influence the concentration and the isolation of MT from molluscan tissu es. Remarkable variations in MT isolation and quantification might depend o n the purification and storage protocol. Because of possible artefacts due to the isolation procedure the establishment of a standard protocol for MT quantification in marine mollusc is still an important goal. In a few speci es the presence of very low molecular weight metal binding ligands has also been reported, in these cases it cannot be excluded that the native MT has been cleaved by the action of proteases. This review aims to report: 1) im portance of a standard method for MT purification and quantification in mol luscs; 2) distribution of MT among molluscan species; 3) data concerning oy ster's and mussel's MTs which are the two more deeply investigated marine m olluscs; 4) biotic and abiotic factors influencing MT concentration, and 5) biological role of MT and use of MT as a biochemical marker of heavy metal pollution.