Substrate‐induced conformational changes in sarcoplasmic reticulum Ca2+‐ATPase probed by surface modification using diethylpyrocarbonate with mass spectrometry

Abstract We have identified 15 residues from the surface of sarcoplasmic reticulum Ca 2+ -pump ATPase, by mass spectrometry using diethylpyrocarbonate modification. The reactivity of 9 residues remained high under all the conditions. The reactivity of Lys-515 at the nucleotide site was severely inhibited by ATP, whereas that of Lys-158 in the A-domain decreased by one-half and increased by five-fold in the presence of Ca 2+ and MgF 4 , respectively. These are well explained by solvent accessibility, p K a and nearby hydrophobicity of the reactive atom on the basis of the atomic structure. However, the reactivity of 4 residues near the interface among A-, N- and P-domain suggested larger conformational changes of these domains in membrane upon binding of Ca 2+ (Lys-436), ATP (Lys-158) and MgF 4 (His-5, -190, Lys-436).