Metallothioneins (MTs) in marine molluscs

The presence of MTs in marine molluscs was firstly hypothesized in oyster and in mussel during the seventies, however mussel's and oysters' MTs were completely purified and sequenced rather later. Already from the first studies 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 monomeric and a dimeric form. Several physiological and biochemical parameters can influence the concentration and the isolation of MT from molluscan tissues. Remarkable variations in MT isolation and quantification might depend on 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 species 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) importance of a standard method for MT purification and quantification in molluscs; 2) distribution of MT among molluscan species; 3) data concerning oyster's and mussel's MTs which are the two more deeply investigated marine molluscs; 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.