Binding of Ca(II), Mg(II), and Zn(II) by 7S fraction of soybean proteins.

Binding of Ca(ll) or Mg(II) by 7s protein at pH 7.8 appears to occur at the imidazole groups of the
histidine residues of the protein molecule. Zn(II) binding at pH 6.5 also occurs at imidazole groups.
The 78 protein binds more Ca(ll) or Mg(II) in borate buffer than in Tris·HCI buffer of the same pH.
Rate of proteolysis, fluorescence, optical rotatory dispersion, and circular dichroism measurements do
not indicate any conformational change in the protein due to metal ion binding. Ca(Il), Mg(Il), or Zn(II)
increases the heat coagulation of 7s protein. At room temperature the protein is precipitated to an
extent of 40% by Ca(ll), 10% by Mg(lI), and 90% by Zn(II). NaCI (0.5 M) suppresses precipitation
by Ca(ll) or Mg(II) and decreases only slightly precipitation by Zn(ll).