Lack of Gross Protein Structure Changes in the Working Cycle of (Na+, K+)‐Dependent Adenosinetriphosphatase

Abstract

IR and tryptophan fluorescence spectra of practically all sufficiently stable functional complexes of a highly purified preparation of membrane-bound (Na+, K+)-dependent ATPase [from pig renal medulla] were measured. The formation of any functional complex was not accompanied by any considerable change of either shape or position of the tryptophan fluorescence spectrum. Only in the presence of adenine nucleotides was there a small decrease of fluorescence intensity (by 5-8%), which apparently results from a change of the sample light scattering. An environment of no more than 1 or a few tryptophan residues may differ in all the (Na+, K+)-ATPase complex studies. A comparison of IR protein spectra in the region of amide I band showed that at any wave number the differences between them did not exceed 3% of the maximum absorption. This means that no more than 3% of protein peptide groups can change their conformation upon transition between the enzyme functional states. These results, obtained by 2 independent techniques, showed that even if changes of the internal protein structure occur during the working cycle of this transport system, they have an extremely local character.