Calorimetric experiments of Mn2+ -binding to alpha-lactalbumin.
We measured by batch microcalorimetry the standard enthalpy change delta H degrees of the binding of Mn2+ to apo-bovine alpha-lactalbumin; delta H degrees = -90 +/- k J.mol-1. The binding constants, KMn2+, calculated from the calorimetric and circular dichroism titration curves, are (4.6 +/- 1).10(5) M-1 and (2.1 +/- 0.4).10(5) M-1, respectively. Batch calorimetry confirms the competitive binding Ca2+, Mn2+ and Na+ to the same site. The relatively small enthalpy change for Mn2+ binding compared to Ca2+ binding favours a model of a rigid and almost ideal Ca2+-complexating site, different from the well-known EF-hand structures. Cation binding to the high-affinity site most probably triggers the movement of an alpha-helix which is directly connected to the complexating loop.
Desmet
J
J
Interdisciplinary Research Centre, University of Leuven, Kortrijk, Belgium.
Van Cauwelaert
F
F
D001665:Binding Sites; D001667:Binding, Competitive; D002151:Calorimetry; D002412:Cations; D002942:Circular Dichroism; D007768:Lactalbumin / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D011487:Protein Conformation; D012964:Sodium / Q000378:metabolism; D013816:Thermodynamics
D002412:Cations; D008345:Manganese; D007768:Lactalbumin; D012964:Sodium