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Abstract

In order to investigate the high‐affinity K⁺ binding to proteins, alkali ion binding studies were performed on a fluorescent derivative of membrane‐bound Na,K‐ATPase in buffered aqueous solution at 37°C employing a specially designed automatic spectrofluorometric titration system. The comparison of the obtained apparent stability constants, which reached values for K⁺ even over 10⁴ M⁻¹ with those of a simpler cyclic peptide, acting as a suitable model compound, provides suggestions concerning the molecular nature of the binding sites involved.