Metallothionein Estimates in Marine Mammal and Fish Tissues by Three Methods:203Hg Displacement, Polarography and Metal-Summation

An 203Hg displacement, polarography and the metal-summation method were used to determine metalloproteins, including metallothionein, in narwhal (Monodon monoceros) liver and kidney, sucker (Catosionws commersonii) and lake trout (Salvelinus namaycush) liver after sample fractionation by gel chromatography and ion-exchange chromatography. Metallothionein in marine mammal tissues was high in cadmium and low in copper, and in fish liver it was high in copper and non-detectable in cadmium. Two methods, polarography and metal-summation were in good agreement with each other for mammalian tissues. The mercury displacement results were significantly higher relative to the other two methods. After ion-exchange chromatography of the tissue cytosols, metallothioneins were determined by three different methods, and were subjected to linear regression analysis. The three methods were highly correlated, with a linear slope of 1 between polarography and metal summation, but less than I between the mercury displacement and the otheir methods. Neither of the methods distinguished metallothionein from other thiolic metalloproteins. Any of the three methods were capable of measuring a relative change in tissue metallothionein with only a modest degree of prior separation, but the determination of absolute levels of metallothionein in mammalian tissues requires; taking into account the positive bias of the mercury displacement. For fish-liver metallothionein there was good agreement between the mercury displacement and the metal summation method.