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Self‐association of plasma membrane Ca 2+ ‐ATPase by volume exclusion
Author(s) -
Kosk-Kosicka Danuta,
Lopez Maria M.,
Fomitcheva Ioulia,
Lew Virgilio L.
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)00870-f
Subject(s) - calmodulin , monomer , chemistry , dimer , enzyme , membrane , atpase , biophysics , fluorescence , biochemistry , biology , organic chemistry , polymer , physics , quantum mechanics
At enzyme concentrations above 40 nM the configuration of the purified plasma membrane Ca 2+ ‐ATPase is that of calmodulin‐insensitive dimers. Dilution of the enzyme generates progressively higher proportions of calmodulin‐sensitive monomers with lower V max and Ca 2+ sensitivity than the dimeric enzyme. Dimerization from monomeric state had not been documented before. We investigated whether concentration by volume exclusion, obtained by addition of a large molecular weight dextran to a monomeric Ca 2+ ‐ATPase would elicit dimer‐like behavior. Dextran induced self‐association of monomers, as monitored by fluorescence energy transfer, but the Ca 2+ sensitivity of the re‐associated monomers was lower than that of the native dimers. These results suggest that the self‐association reaction is structurally but not functionally reversible, and also document the existence of a hitherto unknown kinetic state of the oligomerized Ca 2+ ‐ATPase, with high V max but low Ca 2+ ‐sensitivity.