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Effects of Ca2+, Mg2+ and calmodulin on the formation and decomposition of the phosphorylated intermediate of the erythrocyte Ca2+-stimulated ATPase.
- Source :
-
The Biochemical journal [Biochem J] 1987 Jun 15; Vol. 244 (3), pp. 617-23. - Publication Year :
- 1987
-
Abstract
- Formation of the phosphorylated intermediate (ECaP) of the human erythrocyte Ca2+-stimulated ATPase (Ca2+-ATPase) was more rapid and reached steady state sooner at 400 microM-Ca2+ than at 1 microM-Ca2+. Calmodulin increased the apparent rate of ECaP formation at 1 microM-Ca2+, whereas at 400 microM-Ca2+, calmodulin decreased the steady-state level of the ECaP without affecting its apparent rate of formation. Removal of endogenous Mg2+ with trans-1,2-diaminocyclohexane-NNN'N'-tetra-acetic acid, which decreased both the velocity and Ca2+-sensitivity of the Ca2+-ATPase, did not alter the Ca2+-sensitivity or the apparent rate of formation of ECaP. ECaP formation at high Ca2+ concentrations was not affected by Mg2+ concentrations as high as 1 mM, and the ECaP could be dephosphorylated by ADP and ATP along either the forward or reverse pathways. The results suggest that high Ca2+ concentrations inhibit Ca2+-ATPase activity by preventing dephosphorylation of the E2P complex, rather than by inhibition of the transformation from E1CaP ('high-Ca2+-affinity' ECaP) to E2CaP ('lower-energy' ECaP).
- Subjects :
- Adenosine Diphosphate pharmacology
Adenosine Triphosphate pharmacology
Calcium-Transporting ATPases antagonists & inhibitors
Humans
Macromolecular Substances
Phosphoproteins metabolism
Phosphorylation
Calcium pharmacology
Calcium-Transporting ATPases blood
Calmodulin pharmacology
Erythrocyte Membrane enzymology
Magnesium pharmacology
Subjects
Details
- Language :
- English
- ISSN :
- 0264-6021
- Volume :
- 244
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- The Biochemical journal
- Publication Type :
- Academic Journal
- Accession number :
- 2965571
- Full Text :
- https://doi.org/10.1042/bj2440617