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Calcium‐ and Calmodulin‐Dependent Phosphorylation of Diphosphoinositide in Acetylcholine Receptor‐Rich Membranes from Electroplax of Narke japonica
Author(s) -
Hayashi Fumio,
Amakawa Taisaku
Publication year - 1985
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1985.tb05483.x
Subject(s) - calmodulin , membrane , kinase , trifluoperazine , phosphorylation , chemistry , calcium , biochemistry , inositol , receptor , enzyme , organic chemistry
The phosphoryiation of phosphoinositides in the acetylcholine receptor (AChR)‐rich membranes from the electroplax of the electric fish Narke japonica has been examined. When the AChR‐rich membranes were incubated with [γ‐ 32 P]ATP, 32 P was incorporated into only two inositol phospholipids, i.e., tri‐ and diphosphoinositide (TPI and DPI). Even after the alkali treatment of the membrane, AChR‐rich membranes still showed a considerable DPI kinase activity upon addition of exogenous DPI. It is likely that the 32 P‐incorporation into these lipids was realized by the membrane‐bound DPI kinase and phosphatidyl inositol (PI) kinase. Such a membrane‐bound DPI kinase was activated by Ca 2+ (>10 − ‐ 6 M ), whereas the PI kinase appeared to be inhibited by Ca 2+ . The effect of Ca 2+ on the DPI phosphorylation was further enhanced by the addition of ubiquitous Ca 2+ ‐depen‐dent regulator protein calmodulin. Calmodulin antagonists such as chlorpromazine (CPZ), trifluoperazine (TFP), and N ‐(6‐aminohexyl)‐5‐chloro‐l‐naphthalenesul‐fonamide (W‐7) inhibited the phosphorylation of DPI in the AChR‐rich membranes. It is suggested that the small pool of TPI in the plasma membrane is replenished by such Ca 2+ – and calmodulin‐dependent DPI kinase responding to the change in the intracellular Ca 2+ level.