Binding of Mg(II) by the 11S fraction of soybean proteins.

Binding of Mg(II) by the 11s fraction of soybean
proteins has been measured in 0.1 M borate buffer
of pH 7.8 by equilibrium dialysis. The binding
sites are possibly the imidazole groups of the histidine
residues of the protein molecule. NaCl at
0.5 M concentration suppresses binding. Addition
of utea or .prior treatment of the protein with
EDTA reduces binding, EDTA treatment causes
dissociation of the proteiD which is partly re-versed by the addition of Mg(II). No confonnational
change occurs in the protein due to the
binding of Mg(II). The protein, both before and
after EDTA treatment, is quantitatively precipitated
by 1 x 10-2 M Mg(II). NaCI at 0.5 M concentration
suppresses precipitation. Addition of
Mg(II) to tbe water extract of defatted soybean
yields a precipitate which consists almost entirely
of the 11S fraction.