The Plasma Membrane Calcium Pump
The Ca pump of plasma membranes is an ATPase that has a high affinity for Ca (K m 0.5µM or less) and thus it interacts with it even at the normal low cytosolic concentration (about 0.2µM). The ATPase can therefore be considered as a fine regulator of cell Ca, as opposed to the other Ca-exporting system, the Na/Ca exchanger, which is particularly active in excitable tissues, and handles much larger amounts of Ca with lower affinity. A number of regulators of potential physiological significance modulate (i.e., activate) the ATPase, among them calmodulin (Jarret and Penniston, 1987; Gopinath and Vincenzi, 1987), acidic phos pholipids and polyunsaturated fatty acids (Niggliet al., 1981), and a cAMP-dependent phosphorylation reaction (Neyseset al., 1985). Of interest, although probably not significant physiologically, is the activation of the ATPase by a controlled exposure to proteases like trypsin (Taverna and Hanahan, 1980; Sarkadiet al., 1980).
KeywordsATPase Activity Erythrocyte Membrane Cell Calcium Calmodulin Binding Excitable Tissue
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