Direct demonstration of structural changes in soluble, monomeric Ca2+-ATPase associated with Ca2+ release during the transport cycle.
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 have been examined at pH 8.0, 2 degrees 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)-adenosine diphosphate 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. This is in accordance with the tryptic degradation pattern that suggests proximity between the phosphorylation site and Ca2+ transport sites on the peptide. The structural changes occurring in the soluble monomeric Ca2+-ATPase show that a single polypeptide chain is the functional unit in energy transduction.
Andersen
J P
JP
Jørgensen
P L
PL
Møller
J V
JV
D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D005456:Fluorescent Dyes; D007700:Kinetics; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D011485:Protein Binding; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014357:Trypsin
D005456:Fluorescent Dyes; D010446:Peptide Fragments; D000244:Adenosine Diphosphate; C036745:2',3'-(O-(2,4,6-trinitrocyclohexadienylidine))adenosine 5'-diphosphate; D014357:Trypsin; D000252:Calcium-Transporting ATPases; D002118:Calcium