Cation Binding in Na,K-ATPase, Investigated by 205T1 Solid-State NMR Spectroscopy.

Cation binding to Na,K-ATPase is characterized in native membranes at room temperature by solid-state NMR spectroscopy using the K+ congener 205Tl. It has been demonstrated that the signals from occluded Tl+ and nonspecifically bound Tl+ can be detected and distinguished by NMR. Effects of dipole-dipole coupling between ¹H and 205Tl in the occlusion sites show that the ions are rigidly bound, rather than just occluded. Furthermore, a low chemical shift suggests occlusion site geometries with a relatively small contribution from carboxylate and hydroxyl groups. Nonspecific binding of Tl+ is characterized by rapid chemical exchange, in agreement with the observed low binding affinity. [ABSTRACT FROM AUTHOR]