CHARACTERIZATION OF METALLOTHIONEIN-LIKE PROTEINS FROM ZEBRA MUSSELS (DREISSENA-POLYMORPHA)

Zebra mussels (Dreissena polymorpha) are freshwater mollusks that have recently infested the Great Lakes ecosystem. Possessing a large capac ity for filtration, these mussel populations act as bioconcentrators f or contaminants, such as heavy metals, found in the Great Lakes ecosys tem. Metallothionein is a low-molecular-weight, heavy metal-binding pr otein found in most living organisms. Characterization and partial pur ification of metallothionein-like Cd-binding proteins from zebra musse ls were performed. Zebra mussels were exposed to 500 mu g/L Cd for 14 d. During the exposure period, two mussels were removed on alternate d ays for analysis of Cd-binding proteins. Gel-filtration high-performan ce liquid chromatography-microatomization-atomic absorption spectropho tometry results showed a single Cd-binding molecular weight protein fr action after 2 d of Cd exposure. After 10 d of Cd exposure, however, m ussels exhibited an additional, higher molecular weight, Cd-binding pr otein fraction. The lower molecular weight metallothionein-like Cd-bin ding protein was further isolated and purified by acetone fractionatio n, Sephadex G75, and diethylaminoethyl anion-exchange chromatography. The quantities of Zn, Cu and Cd in the anion-exchange metallothionein- like protein isoforms were determined by inductively coupled plasma-ma ss spectrometry. The ability to bioconcentrate heavy metals in a metal lothionein-like form coupled with their large population in the Great Lakes make zebra mussels suitable for use in a freshwater biomonitorin g program for aquatic metal contamination.