Kinetics of conformational changes induced by the binding of various metal ions to bovine alpha-lactalbumin.
The kinetic effects of the binding of various metal ions (Ca(2+), Cd(2+), Co(2+), Mg(2+), Mn(2+), Sr(2+) and Zn(2+)) to apo bovine alpha-lactalbumin has been monitored by means of stopped-flow fluorescence spectroscopy. Our results show that the measured rate constant for the binding of metal ions to the Ca(2+)-site increases with increasing binding constant. This is, however, not the case for metal ions binding to the Zn(2+)-site. The binding experiments performed at different temperatures allowed us to calculate the activation energy for the transition from the metal-free to the metal-loaded state of the protein. These values do not depend on the nature of the metal ion but are correlated with the type of binding site. As a result, we were able to demonstrate that Mg(2+), a metal ion which was thought to bind to the Ca(2+)-site, shows the same binding characteristics as Co(2+) and Zn(2+) and therefore most likely interacts with the residues belonging to the Zn(2+)-binding site.
Noyelle
Katrien
K
Interdisciplinary Research Centre, K.U. Leuven Campus Kortrijk, E. Sabbelaan 53, B-8500 Kortrijk, Belgium.
Van Dael
Herman
H
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D007700:Kinetics; D007768:Lactalbumin / Q000737:chemistry / Q000378:metabolism*; D008670:Metals / Q000378:metabolism* / Q000494:pharmacology; D011487:Protein Conformation / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics
D008670:Metals; D007768:Lactalbumin