Identification of a cross‐linked double‐peptide from the catalytic site of the Ca²⁺‐ATPase of sarcoplasmic reticulum formed by the Ca²⁺‐ and pH‐dependent reaction with ATP γP‐imidazolidate

The Ca(2+)-ATPase from sarcoplasmic reticulum can be inhibited by the Ca(2+)- and pH-dependent reaction with ATP gamma P-imidazolidate. The chemically and monofunctionally activated inhibitor introduces an intramolecular cross-link between two neighbouring peptides of the active site. This can be followed by the reduced mobility of the ATPase upon SDS-PAGE analysis which becomes even more pronounced after limited trypsinolysis. After cleavage of the cross-linked ATPase molecule by cyanogen bromide and separation of the peptides a double-peptide can be detected which upon sequencing can be identified as part of the phosphorylation and the nucleotide binding site, respectively.