The binding of zinc to the plasma of winter flounder (Pseudopleuronectes americanus): affinity and specificity

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Abstract
The binding affinity of winter flounder plasma proteins for zinc was determined by equilibrium dialysis. The relationship between the percentage of zinc bound and the total zinc present in the system produced a curved line. A Rosenthal type plot indicated that there was more than one binding system for zinc present. The association constant computed from the first slope, 107–108, compared with that of mammalian serum albumin. It required twice the normal total plasma zinc concentration to saturate the higher affinity binding system.All of the plasma zinc could be removed by dialyzing with 10−2M histidine.The specificity of the plasma proteins for binding zinc was studied by introducing the following cations: Cu2+, Cd2+, Ca2+, Mg2+, Co2+, Mn2+, Hg2+, Fe2+, Cr2+, and Ni2+. Only Cu2+ competed significantly with the binding of zinc to the plasma. This competitive effect was diminished in the presence of Tris buffer.Studies in the presence of EDTA indicated that the EDTA had a greater effect on the zinc binding than would be predicted from its theoretical binding capacity for zinc.

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