Comparison of the binding of Ca2+ and Mn2+ to bovine alpha-lactalbumin and equine lysozyme.
The enthalpy change of the binding of Ca2+ and Mn2+ to equine lysozyme was measured at 25 degrees C and pH 7.5 by batch microcalorimetry: delta H degrees Ca2+ = -76 +/- 5 kJ mol-1, delta H degrees Mn2+ = -21 +/- 10 kJ mol-1. Binding constants, log KCa2+ = 6.5 +/- 0.2 and log KMn2+ = 4.1 +/- 0.5, were calculated from the calorimetric data. Therefore, delta S degrees Ca2+ = -131 +/- 20 JK-1 mol-1 and delta S degrees Mn2+ = 8 +/- 44 JK-1 mol-1. Removal of Ca2+ induces small but significant changes in the circular dichroism spectrum, indicating the existence of a partially unfolded apo-conformation, comparable with, but different from, the apo-conformation of bovine alpha-lactalbumin.
Desmet
J
J
Interdisciplinair Research Center, K.U. Leuven Campus Kortrijk, Belgium.
Van Dael
H
H
Van Cauwelaert
F
F
Nitta
K
K
Sugai
S
S
D000818:Animals; D001051:Apoenzymes / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002151:Calorimetry / Q000379:methods; D002417:Cattle; D002942:Circular Dichroism; D006736:Horses; D007768:Lactalbumin / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D009113:Muramidase / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics
D001051:Apoenzymes; D008345:Manganese; D007768:Lactalbumin; D009113:Muramidase; D002118:Calcium