A new possible regulatory system for protein phosphorylation in human peripheral lymphocytes. II. Possible relation to phosphatidylinositol turnover induced by mitogens.
A new possible regulatory system for protein phosphorylation in human peripheral lymphocytes. II. Possible relation to phosphatidylinositol turnover induced by mitogens.
复制标题
人外周淋巴细胞中蛋白质磷酸化的新可能调节系统。
作者：
Y. Ku;A. Kishimoto;Y. Takai;Y. Ogawa;S. Kimura;Y. Nishizuka
人外周淋巴细胞中存在的 Ca++ 激活的磷脂依赖性蛋白激酶除了磷脂外还需要少量的二酰基甘油，特别是在 Ca++ 浓度较低的情况下。这种二酰基甘油必须至少在2位含有不饱和脂肪酸。饱和二酰基甘油如二棕榈精和二硬脂精的效果要差得多。动力学分析表明，不饱和二酰基甘油大大增加了酶对磷脂的表观亲和力，并将 Ca++ 浓度急剧降低至微摩尔范围，从而产生最大的酶活化。在测试的各种磷脂中，磷脂酰丝氨酸在支持酶活性方面最活跃。磷脂酰肌醇和磷脂酰乙醇胺效果较差。磷脂酰胆碱、磷脂酸、鞘磷脂和溶血磷脂酰胆碱是惰性的。因此，最有可能的是，各种淋巴细胞有丝分裂原诱导磷脂酰肌醇的特异性水解，产生这种活性不饱和二酰甘油，其反过来又充当选择性激活这种独特蛋白激酶的第二信使。地布卡因和氯丙嗪似乎与磷脂相互作用，从而抑制该酶的激活过程。环核苷酸依赖性蛋白激酶对这些磷脂相互作用药物不敏感。
Ca++-activated, phospholipid-dependent protein kinase present in human peripheral lymphocytes requires a small amount of diacylglycerol in addition to phospholipid, particularly at lower concentrations of Ca++. It is necessary that such diacylglycerol contain unsaturated fatty acid at least at position 2. Saturated diacylglycerols such as dipalmitin and distearin are far less effective. Kinetic analysis indicates that unsaturated diacylglycerol greatly increases the apparent affinity of the enzyme for phospholipid, and sharply decreases the Ca++ concentration to the micromolar range that gives rise to the maximum enzyme activation. Among various phospholipids tested, phosphatidylserine is most active in supporting enzymatic activity. Phosphatidylinositol and phosphatidylethanolamine are less effective. Phosphatidylcholine, phosphatidic acid, sphingomyelin, and lysophosphatidylcholine are inert. It is most likely, therefore, that various lymphocyte mitogens induce specific hydrolysis of phosphatidylinositol to produce such an active unsaturated diacylglycerol, which in turn serves as a second messenger for the selective activation of this unique protein kinase. Dibucaine and chlorpromazine appear to interact with phospholipid and thereby inhibit the activation process of this enzyme. Cyclic nucleotide-dependent protein kinases are not susceptible to these phospholipid-interacting drugs.