Proton Spin-Echo Spectra of the Isolated Beta Subunit of the CF₀-CF₁ ATP Synthase

Abstract

The application of spin-echo methods (1) in NMR provides a means of selecting resonances on the basis of spin-spin relaxation, which in turn is related to the mobility of residues or molecules involved. Spin-echo spectroscopy has been applied previously in this laboratory to the selective observation of mobile amino acid sidechains on CF₁, the proton translocating ATPase of the chloroplast thylakoid membrane (2, 3). These experiments have demonstrated the existence of a small subset of amino acid sidechains, approximately 25 in number, which extend into the aqueous phase and exhibit mobility much higher that that of the protein as a whole. Two of the sidechains, one aspartate and one glutamate, are immobilized in a highly selective manner by nucleotide binding to the active site. The immobilized groups lie at a distance of approximately 15Â from the metal cofactor bound at the active site.