Abstract
A multiplicity of polypeptides associated with plasma membranes and intracellular membranes of suspension-cultured Italian ryegrass ( Lolium multiflorum Lam.) endosperm cells are phosphorylated by protein kinases associated with the respective membrane preparations. Most of the polypeptide phosphorylations are independent of Ca 2+. The phosphorylations of 14 kD and 13 kD polypeptides in plasma membrane preparations are Ca 2+-dependent as are the phosphorylations of 18 kD, 16 kD and 14.5 kD polypeptides in preparations of intracellular membranes. High molecular mass (> 300 kD) polypeptides in both membrane preparations are also phosphorylated in Ca 2+-dependent reactions. The phenothiazine-derived calmodulin antagonists fluphenazine and chlorpromazine stimulate and La 3+ inhibits polypeptide phosphorylation in both membrane preparations. The major Ca 2+-dependent plasma membrane and intracellular membrane protein phosphorylation reactions are maximally activated at free Ca 2+ concentrations between 0.4 and 10 μM.
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