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Stimulation of plant plasma membrane Ca 2+ ‐ATPase activity by acidic phospholipids
Author(s) -
Bonza Maria Cristina,
Luoni Laura,
De Michelis Maria Ida
Publication year - 2001
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.2001.1120303.x
Subject(s) - phosphatidylinositol , phosphatidylethanolamine , phosphatidic acid , atpase , biochemistry , phosphatidylserine , chemistry , phosphatidylcholine , phospholipid , calmodulin , vesicle , trypsin , enzyme , membrane , signal transduction
The effect of phospholipids on the activity of the plasma membrane (PM) Ca 2+ ‐ATPase was evaluated in PM isolated from germinating radish ( Raphanus sativus L. cv. Tondo Rosso Quarantino) seeds after removal of endogenous calmodulin (CaM) by washing the PM vesicles with EDTA.
Acidic phospholipids stimulated the basal Ca 2+ ‐ATPase activity in the following order of efficiency: phosphatidylinositol 4,5‐diphosphate (PIP2)≈phosphatidylinositol 4‐monophosphate>phosphatidylinositol≈phosphatidylserine≈phosphatidic acid. Neutral phospholipids as phosphatidylcholine and phosphatidylethanolamine were essentially ineffective. When the assays were performed in the presence of optimal free Ca 2+ concentrations (10 μ M ) acidic phospholipids did not affect the Ca 2+ ‐ATPase activated by CaM or by a controlled trypsin treatment of the PM, which cleaved the CaM‐binding domain of the enzyme. Analysis of the dependence of Ca 2+ ‐ATPase activity on free Ca 2+ concentration showed that acidic phospholipids increased V max and lowered the apparent K m for free Ca 2+ below the value measured upon tryptic cleavage of the CaM‐binding domain; in particular, PIP2 was shown to lower the apparent K m for free Ca 2+ of the Ca 2+ ‐ATPase also in trypsin‐treated PM.
These results indicate that acidic phospholipids activate the plant PM Ca 2+ ‐ATPase through a mechanism only partially overlapping that of CaM, and thus involving a phospholipid‐binding site in the Ca 2+ ‐ATPase distinct from the CaM‐binding domain. The physiological implications of these results are discussed.