Role of polyphosphoinositide synthesizing enzyme in intracellar signal transduction system

众所周知，各种激素和自育激素增强肌醇磷脂代谢，导致各种细胞反应。在这种情况下，磷脂酰肌醇4，5-二磷酸（TPI）降解为二酰基甘油和肌醇1，4，5-三磷酸被认为是主要事件。但是，由于TPI以痕量存在，因此其消耗非常迅速。因此，由磷脂酰肌醇（PI）快速代偿性再合成TPI是维持激素反应所必需的。这一步由两种激酶催化，PI激酶和磷脂酰肌醇4-磷酸（DPI）激酶。用Affigel-Blue、DEAE-Biogel、Sephacryl 300、ATP-亲和层析和Mono Q柱层析从大鼠脑中纯化PI激酶。分子量为120，000道尔顿，比活性提高了1250倍，最适pH为7.0，活性需要<Mg^（2+）>。该酶只能磷酸化PI，而不能磷酸化DPI或甘油二酯。

It has been well known that various hormones and autacoids enhance the inositol phospholipids metabolism, leading to various cellular responses. In this case, the degradation of phosphatidylinositol 4, 5, -bisphosphate(TPI) to diacylglycerol and inositol 1, 4, 5,-trisphosphate has been proposed to be a primary event. But, since TPI is present as a trace amount, it becomes to be depletion very rapidly. Therefore, very rapid compensatory resynthesis of TPI from phosphatidylinositol(PI) is necessary to continue the hormonal responses. This step was catalyzed by two kinases,PI kinase and phosphatidylinositol 4-phosphate(DPI) kinase.We tried to purify the enzymes and classify the characterization of them. PI kinase was purified from rat brain, by Affigel-Blue, DEAE-Biogel, Sephacryl 300, ATP-affinity and Mono Q column chromatography. Molecular weight was found to be 120,000 dalton and the specific activity increased 1250-fold, optimal pH was 7.0 and <Mg^(2+)> was required for the activity. The enzyme can only phosphorylate PI but not DPI or diacylglycerol.