Binding strength of calcium ion to bovine alpha-lactalbumin.
A Ca2+-sensitive electrode was used for determination of the binding strength of Ca2+ to bovine alpha-lactalbumin in 60 mM Tris buffer (pH 7.8-8.5) in the presence of various concentrations of NaCl. The dependence of the apparent binding constant on the concentration of NaCl was consistent with competitive binding of Ca2+ and Na+, and the binding constants of Ca2+ and Na+ were found to be 2.2 (+/- 0.5) X 10(7) M-1 and 99 (+/- 33) M-1, respectively, at 37 degrees C and pH 8.0. The temperature dependence of the binding constant of Ca2+ was examined between 30 and 45 degrees C; extrapolation of the dependence led to a binding constant of approximately 1 X 10(8) M-1 at pH 8.4 and 25 degrees C. The electrostatic contribution and conformational effect of the protein were also taken into consideration, and the intrinsic binding constant of Ca2+ to native alpha-lactalbumin was calculated to be (1.2-1.5) X 10(10) M-1 at 37 degrees C and pH 8.0.
D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000032:analysis*; D002417:Cattle; D004566:Electrodes; D007768:Lactalbumin / Q000032:analysis*; D008433:Mathematics; D008956:Models, Chemical; D011199:Potentiometry; D011485:Protein Binding; D012964:Sodium / Q000032:analysis; D013696:Temperature
D007768:Lactalbumin; D012964:Sodium; D002118:Calcium