Sackett DL, Kosk-Kosicka D. The active species of plasma membrane Ca2+-ATPase are a dimer and a monomer-calmodulin complex.
J Biol Chem 1996;
271:9987-91. [PMID:
8626638 DOI:
10.1074/jbc.271.17.9987]
[Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The purified plasma membrane Ca2+-ATPase is fully activated through the enzyme concentration-dependent self-association at physiologically relevant Ca2+ concentrations (Kosk-Kosicka, D., and Bzdega, T. (1988) J. Biol. Chem. 263, 18184-18189; Kosk-Kosicka, D., Bzdega, T., and Wawrzynow, A. (1989) J. Biol. Chem. 264, 19495-19499). We have previously shown that the Ca2+-ATPase activity of the oligomeric enzyme is independent of calmodulin, in contrast to another active enzyme species, a presumable monomer, that is activated by calmodulin binding. Presently, we have succeeded in determining the molecular mass of the two active enzyme species by equilibrium ultracentrifugation. For the calmodulin-dependent species, the molecular mass is 170 +/- 30 kDa, which is consistent with predominantly monomeric Ca2+-ATPase with bound calmodulin. The molecular mass of calmodulin-independent oligomers is 260 +/- 34 kDa, indicating that they are dimers. Results of experiments performed under different calcium and potassium concentrations and in the presence of dextran that causes molecular crowding verify a strict Ca2+ requirement of the dimerization process. We conclude that the active species of the Ca2+-ATPase are a monomer-calmodulin complex and a dimer.
Collapse