Mehta V, Namboodiri M A
Department of Biology, Georgetown University, Washington, DC 20057, USA.
Brain Res Mol Brain Res. 1995 Jul;31(1-2):151-7. doi: 10.1016/0169-328x(95)00044-s.
To understand the role of N-acetylaspartate (NAA) as an acetyl donor, we investigated the metabolism of NAA in brain and liver slice preparations. The tissue slices were incubated with [14C-acetyl]NAA (SA = 3 microCi/mumol) or [14C]acetate (SA = 3 microCi/mumol) for 2 h. The tissue was homogenized and was extracted using chloroform/methanol (2:1). The aqueous phase was initially analyzed using anion exchange HPLC while the lipid phase was analyzed using a two-dimensional TLC system. Further resolution of the NAA peak from the anion exchange HPLC was performed using a reverse phase HPLC system. The aqueous phase of both the liver and brain samples incubated with [14C-acetyl]NAA revealed similar patterns of three distinct radioactivity peaks corresponding to NAA, acetate and an early eluting unknown molecule. Further resolution of the NAA peak using reverse phase HPLC indicated that it corresponded to NAA and acetyl CoA. There was significant incorporation of radioactivity into various lipid components in both the brain and liver samples. Patterns similar to that observed with NAA were detected in the case of [14C]acetate in both the brain and liver slice preparations. These results demonstrate that NAA metabolism is not restricted to the nervous system, although its biosynthesis is. It is clear that acetyl moiety of NAA is incorporated into lipids and partially hydrolyzed to free acetate in both brain and liver preparations. Further, production of acetyl CoA from NAA indicates that the acetyl group of NAA is incorporated into lipids and perhaps other acetylated molecules via the acetyl CoA route. A working hypothesis on the metabolic role of NAA is presented.
为了解N-乙酰天门冬氨酸（NAA）作为乙酰供体的作用，我们研究了NAA在脑和肝切片制剂中的代谢情况。将组织切片与[14C-乙酰基]NAA（比活度=3微居里/微摩尔）或[14C]乙酸盐（比活度=3微居里/微摩尔）孵育2小时。将组织匀浆，并用氯仿/甲醇（2:1）提取。水相最初用阴离子交换高效液相色谱分析，而脂质相用二维薄层色谱系统分析。使用反相高效液相色谱系统对阴离子交换高效液相色谱中的NAA峰进行进一步分离。用[14C-乙酰基]NAA孵育的肝和脑样品的水相显示出类似的模式，有三个不同的放射性峰，分别对应NAA、乙酸盐和一个早期洗脱的未知分子。用反相高效液相色谱对NAA峰进行进一步分离表明，它对应于NAA和乙酰辅酶A。在脑和肝样品中，各种脂质成分都有显著的放射性掺入。在脑和肝切片制剂中，[14C]乙酸盐的情况也检测到了与NAA相似的模式。这些结果表明，NAA的代谢并不局限于神经系统，尽管其生物合成是这样。很明显，NAA的乙酰部分在脑和肝制剂中都被掺入脂质并部分水解为游离乙酸盐。此外，NAA生成乙酰辅酶A表明，NAA的乙酰基团通过乙酰辅酶A途径被掺入脂质以及可能的其他乙酰化分子中。本文提出了一个关于NAA代谢作用的工作假说。
