Regulation of phosphatidylinositol kinase activity

磷脂酰肌醇（PI）周转被认为是响应各种激素和生长因子的受体介导的信号传导途径的重要组成部分。在这种情况下，两个推定的第二信使，甘油二酯（DG）和肌醇1，4，5-三磷酸，通过水解磷脂酰肌醇4，5-二磷酸。DG激活蛋白激酶C，而1，4，5-三磷酸肌醇导致细胞内钙库中Ca^<2+>的释放。在分解后，磷脂酰肌醇4，5-二磷酸通过PI激酶和磷脂酰肌醇4-磷酸（PIP）激酶逐步磷酸化PI而迅速再合成，为了阐明PI激酶在PI周转调节中的可能重要性，还需要酶的纯化和表征。在这项研究中，纯化和表征的膜结合形式的PI金 ...更多信息 从大鼠脑组织中分离纯化了一种膜结合型磷脂酰肌醇（PI）激酶。酶用triton X-100从盐洗膜上溶解，纯化11，183倍，最终比活性为150 nmol/min/mg蛋白质。纯化步骤包括使用Q-Sepharose Fast Flow、磷酸纤维素、Toyopolymer HW 55和Affi-Gel Blue的几次色谱。纯化的PI激酶通过凝胶过滤和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳估计分子量为80，000和76，000。纯化的激酶仅磷酸化PI，不磷酸化磷脂酰肌醇4-磷酸或二酰甘油。PI和ATP的Km值分别为115和150 μ M。该酶需要Mg^<2+>（5-20 mM）或Mn^<2+>（1-2 mM）才能发挥活性，0.1-1.0%（w/v）Triton X-100可刺激该酶，0.05%十二烷基硫酸钠可完全抑制该酶。该酶的最适pH值为7.4左右。该酶利用ATP而不是GTP作为磷酸供体。核苷三磷酸而不是ATP和二磷酸显着抑制激酶活性。腺苷、cAMP和槲皮素的抑制作用较弱。少

Phosphatidylinositol (PI) turnover has been thought to be an essential part of receptor-mediated signal transduction pathways in response to various hormones and growth factors. In this case, two putative second messengers, diacylglycerol (DG) and inositol 1,4,5-trisphosphate, are generated through the hydrolysis of phosphatidylinositol 4,5-bisphosphate. DG activates protein kinase C, whereas inositol 1,4,5-trisphosphate causes the release of Ca^<2+> from an intracellular calcium store.Following the breakdown, phosphatidylinositol 4,5-bisphosphate is rapidly resynthesized by stepwise phosphorylation of PI by PI kinase and phosphatidylinositol 4-phosphate (PIP) kinase, and thus the substrate for the generation of second messengers is continuously supplied.To clarify the possible importance of PI kinase in the regulation of PI turnover, purification and characterization of the enzyme is also required. In this study, the purification and characterization of a membrane-bound form of PI kin … More ase from rat brain was carried out.A membrane-bound phosphatidylinositol (PI) kinase was purified from rat brain. The enzyme was solubilized with triton X-100 from salt-washed membrane and purified 11,183-fold, with a final specific activity of 150 nmol/min/mg of protein. Purification steps included several chromatography using Q-Sepharose Fast Flow, cellulose phosphate, Toyopearl HW 55 and Affi-Gel Blue. The purified PI kinase had an estimated molecular weight of 80,000 by gel filtration and 76,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified kinase phosphorylated only PI and did not phosphorylated phosphatidylinositol 4-phosphate or diacylglycerol. K_m values for PI and ATP were found to be 115 and 150 muM, respectively. The enzyme required Mg^<2+>(5-20 mM) or Mn^<2+>(1-2 mM) for activity, was stimulated by 0.1-1.0% (w/v) Triton X-100, and completely inhibited by 0.05% sodium dodecyl sulfate. The enzyme activity showed a broad PH optimum at around 7.4. The enzyme utilized ATP and not GTP as phosphate donor. Nucleoside triphosphates other than ATP and diphosphates significantly inhibited the kinase activity. However, inhibitory effects of adenosine, cAMP, and quercetin were weak. Less