Evidence for two distinct lysophospholipase activities that degrade lysophosphatidylcholine and lysophosphatidic acid in neuronal nuclei of cerebral cortex
Evidence for two distinct lysophospholipase activities that degrade lysophosphatidylcholine and lysophosphatidic acid in neuronal nuclei of cerebral cortex
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DOI：
10.1016/s1388-1981(99)00057-8
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发表时间：
1999-05-18
影响因子：
4.8
通讯作者：
Chang, HY
中科院分区：
文献类型：
--
作者：
Baker, RR;Chang, HY
从未成熟的兔大脑皮质分离神经元核，并用两种不同的1-酰基溶血磷脂：溶血磷脂酰胆碱(LysoPC)和溶血磷脂酸(LysoPA)研究核溶血磷脂酶活性。我们对这两种溶质脂的兴趣来自于观察到lysoPA可以通过以竞争的方式显著抑制非常活跃的核LysoPC溶血磷脂酶活性来促进LysoPC的乙酰化(R.R.Baker，H.-y)。张，莫尔。牢房。生物化学。(1999)在新闻界)。由于也有证据表明有核LysoPA去酰化作用，因此观察一种活性是否可能同时利用两种溶菌脂底物是很有意义的。我们现在有证据表明神经元核中有两种不同的溶血磷脂酶活性。溶血磷脂酶活性较高，在胞核中含量较高，在pH 8.4~9范围内活性最高，而溶血磷脂酶活性在较宽的pH范围内保持不变，游离脂肪酸对溶血磷脂酶活性有明显的抑制作用，血清白蛋白对溶血磷脂酶活性有较大的刺激作用，而溶血磷脂酶活性受这些因素的影响较小。在含有放射性溶血磷脂酶的培养液中加入溶血磷脂酶，对放射性脂肪酸的释放没有明显的抑制作用，说明溶血磷脂酶活性没有利用溶血磷脂酶的底物。在与溶血磷脂酶的孵育中，镁三磷酸腺苷和辅酶A产生了相当大的磷脂酰胆碱，其放射性均匀地分布在sn-1和sn-2位置，这表明既可以直接从溶血磷脂酶底物上标记，也可以从溶血磷脂酶活性产生的脂肪酸中进行标记。相比之下，与放射性溶解PA底物相比，镁-三磷酸腺苷和辅酶A促进了相对较低水平的磷脂酸的形成，其主要标记直接来自放射性溶解PA。在很大程度上是因为核溶血磷脂酶的高活性，在神经元核中有相当大的潜力来限制溶血磷脂酶在其他反应中的使用，例如形成酰基PAF(I-acyl sialogue of PLT Activing Fine)。有趣的是，与脑缺血相关的条件，如游离脂肪酸水平增加，pH下降和镁三磷酸腺苷下降，可能允许保存神经元核溶血酶C水平以进行乙酰化。溶血磷脂酶活性的存在允许对溶血磷脂酶的独立调控，而溶血磷脂酶是核溶血磷脂酶的重要调节因子。(C)1999 Elsevier Science B.V.保留所有权利。
Neuronal nuclei were isolated from immature rabbit cerebral cortex and nuclear lysophospholipase activities studied using two different 1-acyl lysophospholipids: lysophosphatidylcholine (lysoPC) and lysophosphatidic acid (lysoPA). Our interest in these two lysolipids arose from the observation that lysoPA could promote the acetylation of lysoPC by substantially inhibiting a very active nuclear lysoPC lysophospholipase activity, in a competitive manner (R.R. Baker, H.-y. Chang, Mol. Cell. Biochem. (1999) in press). As there was also evidence for nuclear lysoPA deacylation, it was of interest to see whether one activity could possibly utilize both lysolipid substrates. We now have evidence for two separate lysophospholipase activities in neuronal nuclei. The lysoPC lysophospholipase activity was the more active, more highly enriched in the neuronal nuclei, and showed optimal activity at pH 8.4-9, while the lysoPA lysophospholipase activity was maintained over a much broader pH range, The lysoPC activity was substantially inhibited by free fatty acid, and showed considerable stimulation by serum albumin, while the activity utilizing lysoPA was much less affected by these agents. When lysoPC was added to incubations containing radioactive lysoPA, there was no significant inhibition found in rates of release of radioactive fatty acid, indicating that the lysoPA lysophospholipase activity did not utilize the lysoPC substrate. In incubations with lysoPC, MgATP and CoA brought about a sizable formation of phosphatidylcholine whose radioactivity was equally distributed between the sn-1 and sn-2 positions suggesting labelling both directly from the lysoPC substrate and from fatty acid produced by the lysophospholipase activity. By comparison, with the radioactive lysoPA substrate, MgATP and CoA promoted relatively lower levels of phosphatidic acid formation whose principal labelling came directly from the radioactive lysoPA. Largely because of the high activity of the nuclear lysoPC lysophospholipase, there is considerable potential in the neuronal nucleus to limit the use of lysoPC in other reactions, such as the formation of acylPAF (I-acyl analogue of platelet activating factor). It is of interest that conditions associated with brain ischaemia such as increased free fatty acid levels, falling pH and declines in MgATP may allow a preservation of neuronal nuclear lysoPC levels for acetylation. The existence of a separate lysophospholipase activity for lysoPA allows an independent control of lysoPA which can serve as an important regulator of the nuclear lysoPC lysophospholipase. (C) 1999 Elsevier Science B.V. All rights reserved.