Binding of Inorganic Iodide to the Plasma Proteins of Teleost Fishes

Abstract

The natural binding of inorganic iodide by plasma proteins was studied in 10 freshwater teleost fishes, 16 marine teleost fishes, 3 elasmobranchs, 1 amphibian, 1 reptile, 1 bird, 2 mammals, and 2 arthropods. Of these, significant binding existed only in species of the order Clupeiformes including Esox lucius (average 80.9% of plasma inorganic iodide was protein-bound at 20 C), Coregonus clupeaformis (average 80.3% bound), Salmo gairdneri (average 84.3% bound), and Thymallus arcticus (average 81.0% bound). Significant binding was not found in fish of the orders Cypriniformes, Perciformes, Pleuronectiformes, Batrachoidiformes, Gadiformes, Squaliformes, Chimaeriformes, and Rajiformes. Esox lucius and C. clupeaformis showed a small seasonal variation in binding capacity. The plasma of male fish bound significantly more iodide than did the plasma of female fish.Inorganic iodide was found to bind with a plasma albumin-like protein. The binding sites were presumably free cationic groups of basic amino acid residues on the protein molecules. Iodide binding was inhibited by NO3−, SCN−, ClO4−, and CCl3COO−, but not affected by thiourea, thiouracil, and other halide ions. Binding energy was weak in both E. lucius (−5.98 Kcal/mole) and C. clupeaformis (−6.08 Kcal/mole).