Phosphatidylinositol kinase of bovine adrenal chromaffin granules: kinetic properties and inhibition by low concentrations of Ca2+.
The kinetics and regulatory properties of phosphatidylinositol (PI) kinase were studied in chromaffin granule ghosts isolated from the bovine adrenal medulla. Phosphatidylinositol 4-phosphate (PIP) was the major 32P-labelled phospholipid formed when the isolated membranes were phosphorylated by [gamma-32P]ATP. The PI kinase activity was rather independent of pH, but highly dependent on Mg2+ with a maximal stimulation at 60 mM Mg2+. By contrast, KCl and NaCl had a slight inhibitory effect. The Km value for MgATP was 44 and 62 microM in the presence of 1 and 20 mM MgCl2, respectively. The PI kinase was almost fully and reversibly inhibited by free Ca2+ (calmodulin-independent) in the nanomolar and low micromolar range, depending on the concentration of Mg2+. The inhibition was not dependent on Ca2+-stimulated protein phosphorylation, and it could not be explained by a dephosphorylation of PIP.
Husebye
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Department of Biochemistry, University of Bergen, Norway.
Flatmark
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D019870:1-Phosphatidylinositol 4-Kinase; D000313:Adrenal Medulla / Q000201:enzymology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology; D002417:Cattle; D002837:Chromaffin Granules / Q000201:enzymology*; D002838:Chromaffin System / Q000201:enzymology*; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D010766:Phosphorylation; D010770:Phosphotransferases / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism
D002147:Calmodulin; D008563:Membrane Lipids; D010743:Phospholipids; D010770:Phosphotransferases; D019870:1-Phosphatidylinositol 4-Kinase; D008274:Magnesium; D002118:Calcium