Regulation of rat liver cytosolic CTP: phosphocholine cytidylyltransferase by phosphorylation and dephosphorylation.
Regulation of rat liver cytosolic CTP: phosphocholine cytidylyltransferase by phosphorylation and dephosphorylation.
复制标题
大鼠肝细胞质 CTP 的调节：通过磷酸化和去磷酸化的磷酸胆碱胞苷酰转移酶。
DOI：
10.1016/s0021-9258(19)45365-9
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发表时间：
1982
期刊：
影响因子：
--
通讯作者：
D. Vance
中科院分区：
文献类型：
--
作者：
S. Pelech;D. Vance
大鼠肝细胞质CTP：磷酸胆碱胞基转移酶（ec2.7）7.15)细胞质溶胶孵育后活性提高（37℃孵育10分钟1.7倍，20℃孵育5小时5.5倍）。在37℃时，当向细胞质溶胶中加入14mm镁和0.5 m~ ATP时，这种激活以时间和浓度依赖的方式被阻止。用兔肌肉、牛肉和猪心脏的蛋白激酶抑制剂在37℃下滴定10分钟，在Mg-ATP存在的情况下，细胞质被激活5倍，而对照细胞质被刺激2.2倍。在20℃时，20 m~ NaF的存在使胞基转移酶的活性降低了5倍。mg - atp处理的磷脂酰转移酶的K…与对照相比没有变化，尽管底物对磷脂浓度超过1 m~有明显的抑制作用。Mg的K。atp处理的胞基转移酶对CTP的K值高达5 mM，而蛋白激酶抑制剂处理的胞基转移酶K值约为0.35 m~。mg - atp处理后的大鼠全肝磷脂可使胞酰基转移酶活性提高6倍，使CTP的K值降至0.2 mM，而蛋白激酶抑制剂刺激的胞酰基转移酶活性被磷脂降低25%。总的来说，这些数据暗示胞基转移酶是一种易受磷酸化-去磷酸化-去磷酸化循环调节的酶。磷脂酰胆碱在大鼠肝脏和其他系统中主要通过cdp -胆碱途径合成(1)。许多研究已经确定了CTP：磷酸胆碱胞基转移酶（ec2.7）。7.15)作为该途径的关键调节酶（2-13）。这种酶是模棱两可的（14），因为它在肝脏匀浆的细胞质和微粒体中都有恢复（15）。在微粒体中，胞基转移酶位于内质网封闭片段的细胞质侧（16）。酶活性在这些组分之间的分布取决于均质介质和离心方法（17）。当肝脏在0.9% NaCl等渗溶液中均质时，大部分酶活性存在于细胞质部分（18）。新鲜大鼠肝细胞质中胞基转移酶的M值为2 × lo5，并被命名为l型（15）。当细胞溶质
Rat liver cytosolic CTP: phosphocholine cytidylyltransferase (EC 2.7. 7.15) activity was elevated by incubation of cytosol (1.7-fold at 37" C for 10 min or 5.5-fold at 20" C for 5 h). At 37" C, this activation was prevented in a time-and concentration-dependent manner when 14 mM magnesium and 0.5 m~ ATP were added to the cytosol. Titration of cytosol with protein kinase inhibitors from rabbit muscle and beef and porcine heart for 10 min at 37" C permitted a 5-fold activation in the presence of Mg-ATP, while control cytosol was stimulated 2.2-fold. At 20" C, the activation of cytidylyltransferase was reduced &fold by the presence of 20 m~ NaF. The K,,, of the Mg-ATP-treated cytidylyltransferase for phosphocholine was unchanged compared to controls, although substrate inhibition was apparent for phosphocholine concentrations exceeding 1 m~. The K,,, of the Mg. ATP-treated cytidylyltransferase for CTP was as high as 5 mM, while protein kinase inhibitor-treated cytidylyltransferase had a K, of approximately 0.35 m~. The Mg-ATP-treated cytidylyltransferase activity could be elevated 6-fold by phospholipid prepared from total rat liver and the K,,, for CTP reduced to 0.2 mM. In contrast, cytidylyltransferase activity stimulated by protein kinase inhibitor was reduced 25% by phospholipid. Collectively, these data implicate cytidylyltransferase as an enzyme susceptible to regulation by a phosphorylation-dephosphory-lation cycle.Phosphatidylcholine is synthesized primarily via the CDP-choline route in rat liver and other systems (1). Numerous studies have identified CTP: phosphocholine cytidylyltransferase (EC 2.7. 7.15) as a key regulatory enzyme for this pathway (2-13). This enzyme is ambiquitous (14) in that it is recovered in both the cytosolic and microsomal fractions of the liver homogenate (15). In the microsomes, the cytidylyltransferase is located on the cytoplasmic side of the sealed fragments of endoplasmic reticulum (16). The distribution of enzyme activity between these fractions is dependent on the homogenization medium and method of centrifugation (17). When liver is homogenized in isotonic 0.9% NaCl solution, the majority of the enzyme activity resides in the cytosolic fraction (18). The cytidylyltransferase in fresh rat liver cytosol has a M, of 2 X lo5 and has been designated the L-form'(15). When cytosol