Equilibrium and kinetic study of sodium‐and potassium‐induced conformational changes of apo‐α‐lactalbumin

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Abstract
Equilibrium and kinetics of Na+‐and K+‐induced conformational changes of apo‐α‐lactalbumin were studied by means of circular dichroism. While apo‐α‐lactalbumin was considerably unfolded in the absence of Na+ or K+ in 20 mM Tris at pH 8.0 and 25°, both the monovalent cations restored the tertiary structure of the protein. Apparent binding constants of Na+ and K+ to the apoprotein were estimated from the equilibria of the Na+‐ and K+‐induced conformational changes. Based on kinetic data of the conformational changes induced by the monovalent cations, binding mechanism of the ions to the apo‐protein was examined. Bound alkali‐metal ions stabilize the native‐like state and an activated state in the unfolding‐refolding reaction of the apoprotein.