Related Experiment Videos
Ca2+ translocation across sarcoplasmic reticulum ATPase randomizes the two transported ions
1Commissariat à l'Energie Atomique and Unité de Recherche 2096 Associée au Centre National de la Recherche Scientifique, Section de Biophysique des Protéines et des Membranes, Département de Biologie Cellulaire et Moléculaire, Centre d'
The Journal of Biological Chemistry
|August 23, 1996
Summary
Calcium ions binding to the nonphosphorylated ATPase are sequentially dissociated. The study reveals that calcium ion order is not maintained during membrane translocation, indicating mixing during phosphorylation and dephosphorylation.
Area of Science:
- Biochemistry
- Molecular Biology
- Membrane Transport
Background:
- Calcium ions (Ca2+) play crucial roles in cellular signaling and muscle contraction.
- The sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) actively transports Ca2+ across membranes.
- Understanding Ca2+ binding and dissociation dynamics is key to SERCA function.
Purpose of the Study:
- To investigate the sequential dissociation of cytoplasmic Ca2+ from the nonphosphorylated ATPase.
- To determine if a pre-established Ca2+ order is maintained during membrane translocation.
- To elucidate the Ca2+ binding and dissociation mechanisms during ATP-induced phosphorylation and ADP-induced dephosphorylation.
Main Methods:
- Utilized leaky vesicles under specific conditions (5°C, pH 8, 300 mM K+) to accumulate ADP-sensitive phosphoenzyme.
- Investigated Ca2+ dissociation from both cytoplasmic and luminal sides of the ATPase.
- Tracked Ca2+ ion identity and order during membrane translocation.
Main Results:
- Cytoplasmic Ca2+ dissociation from the nonphosphorylated ATPase is sequential.
- Luminal Ca2+ dissociation from the phosphoenzyme is also sequential, with superficial Ca2+ being exchangeable and deeper Ca2+ blocked.
- Ca2+ ion order is not maintained during translocation from cytoplasmic to luminal or luminal to cytoplasmic sides.
Conclusions:
- The two Ca2+ ions are mixed during both ATP-induced phosphorylation and ADP-induced dephosphorylation.
- This mixing suggests a dynamic and non-ordered mechanism for Ca2+ transport by the ATPase.
- The findings contribute to a deeper understanding of the molecular mechanisms governing Ca2+ transport.