Direct demonstration of structural changes in soluble, monomeric Ca2+-ATPase associated with Ca2+ release during the transport cycle.

Publisher Website
Google Scholar
Abstract
The time courses of changes in protein conformation and Ca2+ binding in the phosphorylated state of membrane-bound and soluble monomeric Ca2+-ATPase from sarcoplasmic reticulum were examined at pH 8.0, 2.degree. C. The transition from ADP-sensitive to ADP-insensitive phosphoenzyme occurs in the soluble monomer as well as in membranous Ca2+-ATPase and is accompanied by an increase in fluorescence from 2'',3''-O-(2,4,6-trinitrocyclohexyldienylidine)-ADP bound to the catalytic site and change in tryptic cleavage pattern. A decrease of Ca2+ affinity occurs simultaneously with the fluorescence rise, suggesting a single-step mechanism for energy transfer between the catalytic site and the Ca2+ transport sites. Proximity between the phosphorylation site and Ca2+ transport sites on the peptide is suggested. A single polypeptide chain is the functional unit in energy transduction.