Transition metal-binding proteins from three Chesapeake Bay fish species

Three species of Chesapeake Bay fish were collected, and endogenous levels of metal binding protein (MBP) were determined. In addition, the induction of metal-binding proteins by cadmium was studied. Livers from freshly caught fish were extracted and chromatographed on Sephadex G-75 to resolve MBP in the 5 to 20 kdalton range. All species studied exhibit measurable but varied levels of endogenous MBPs in the molecular weight range investigated, mostly as a copper protein complex. Upon induction with cadmium, the total MBP content increased in both catfish (Ictalurus punctatus) and striped bass (Morone saxatilis), with significant amounts of cadmium bound to the protein. In white perch (Morone americana), induction of MBPs with cadmium could not be demonstrated due to the large amount of constitutive Cu-BP present, although significant quantities of cadmium were bound to MBP. Electrophoresis in polyacrylamide gel was used to further identify these MBPs. Electrochemical analysis of the MBPs by polarography indicated that the wave properties of the fish MBPs resemble that of rat metallothionein. In conclusion, these studies indicate that: MBPs are present in estuarine fish from the Chesapeake Bay; concentrations of MBPs and their inducibility by exogenous cadmium vary with species, and fish MBPs may be related to mammalian metallothionein.