Husebye E S, Flatmark T
Department of Biochemistry, University of Bergen, Norway.
Biochim Biophys Acta. 1988 Feb 22;968(2):261-5. doi: 10.1016/0167-4889(88)90015-8.
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.
对从牛肾上腺髓质分离出的嗜铬粒蛋白颗粒膜中磷脂酰肌醇（PI）激酶的动力学和调节特性进行了研究。当分离的膜用[γ-32P]ATP进行磷酸化时，磷脂酰肌醇4-磷酸（PIP）是形成的主要32P标记磷脂。PI激酶活性相当不依赖于pH，但高度依赖于Mg2+，在60 mM Mg2+时具有最大刺激作用。相比之下，KCl和NaCl有轻微的抑制作用。在存在1 mM和20 mM MgCl2时，MgATP的Km值分别为44和62 μM。PI激酶在纳摩尔和低微摩尔范围内几乎完全且可逆地被游离Ca2+（不依赖钙调蛋白）抑制，这取决于Mg2+的浓度。这种抑制不依赖于Ca2+刺激的蛋白质磷酸化，也不能用PIP的去磷酸化来解释。
