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  • Title: Quantitative analysis of the interaction between the fluorescent probe eosin and the Na+/K+-ATPase studied through Rb+ occlusion.
    Author: Montes MR, González-Lebrero RM, Garrahan PJ, Rossi RC.
    Journal: Biochemistry; 2004 Feb 24; 43(7):2062-9. PubMed ID: 14967046.
    Abstract:
    We report a study on the effect of the fluorescent probe eosin on some of the reactions involved in the conformational transitions that lead to the occlusion of the K(+)-congener Rb(+) in the Na(+)/K(+)-ATPase. Eosin decreases the equilibrium levels of occluded Rb(+), this effect being fully attributable to a decrease in the apparent affinity of the enzyme for Rb(+) since the capacity for occlusion remains independent of eosin concentration. The results can be quantitatively described by a model that assumes that two molecules of eosin are able to bind to the Na(+)/K(+)-ATPase, both to the Rb(+)-free and to the Rb(+)-occluded enzyme regardless of the degree of cation occlusion. Concerning the effect on the affinity for Rb(+) occlusion, transient state experiments show that eosin reduces the initial velocity of occlusion, and that, like ATP, it increases the velocity of deocclusion of Rb(+). Interactions between eosin and ATP on Rb(+)-release experiments seem to indicate that eosin binds to the low-affinity site of ATP from which it exerts effects that are similar to those of the nucleotide.
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