Zinc ion binding to human brain calcium binding proteins, calmodulin and S100b protein

Comparative studies have been performed on the binding properties of zinc ions to human brain calmodulin and S100b protein. Calmodulin is characterized by two sets of Zn2+ binding sites, with KD ranging from 8.10(-5)M to 3.10(-4)M. The S100b protein also exhibited two sets of zinc binding sites, with a much higher affinity. KD = 10(-7) - 10(-6)M. We suggest that S100b protein should no longer be considered only as a "calcium binding protein" but also as a "zinc binding protein", and that Zn2+ ions are involved in the functions of the S100 proteins.