Allan D, Michell R H
Biochem J. 1974 Sep;142(3):591-7. doi: 10.1042/bj1420591.
Phosphatidylinositol breakdown by subcellular preparations of small lymphocytes from pig mesenteric lymph nodes was investigated. Activity was higher than in preparations from the tissues studied previously; it was recovered largely in the soluble fraction, which showed pH optima at both 5.4-5.6 and 7.0-7.3. As in other tissues, phosphatidylinositol cleavage produced 1,2-diacylglycerol and a mixture of myo-inositol 1:2-cyclic phosphate and myo-inositol 1-phosphate. It was stimulated by addition of CaCl(2) and, less effectively, by MgCl(2). On sucrose-density-gradient ultracentrifugation at pH7.0 two peaks of activity were observed (approx. sedimentation coefficients 8S and 10S); the activity profiles on the gradients were similar when assayed at pH7.0 and 5.5. Activity at pH7.0 (and 0.4mm-CaCl(2)) was decreased by agents, such as salts and lipophilic cations, which tend to neutralize the negative charge of phosphatidylinositol; at pH5.5 these agents slightly stimulated activity. It is suggested that the same enzyme(s) may be responsible for activity at both pH optima and that previous workers may have underestimated the pH7.0 activity because of the inhibitory influence of cations under the usual assay conditions.
研究了猪肠系膜淋巴结中小淋巴细胞亚细胞制剂对磷脂酰肌醇的分解作用。其活性高于先前研究的组织制剂；大部分活性存在于可溶性部分，该部分在pH 5.4 - 5.6和7.0 - 7.3时均显示出最适pH值。与其他组织一样，磷脂酰肌醇的裂解产生1,2 - 二酰基甘油以及肌醇1:2 - 环磷酸酯和肌醇1 - 磷酸酯的混合物。添加CaCl₂可刺激其活性，添加MgCl₂的刺激效果稍弱。在pH 7.0条件下进行蔗糖密度梯度超速离心时，观察到两个活性峰（沉降系数约为8S和10S）；在pH 7.0和5.5下测定时，梯度上的活性分布相似。在pH ７.0（以及0.4mM CaCl₂）时，盐和亲脂性阳离子等倾向于中和磷脂酰肌醇负电荷的试剂会降低活性；在pH 5.5时，这些试剂会轻微刺激活性。这表明在两个最适pH值下的活性可能由同一种酶负责，并且由于在通常的测定条件下阳离子的抑制作用，先前的研究人员可能低估了pH 7.0时的活性。
