Burri R, Steffen C, Herschkowitz N
Department of Pediatrics, University of Berne, Switzerland.
Dev Neurosci. 1991;13(6):403-11. doi: 10.1159/000112191.
The function of N-acetyl-L-aspartate (NAA), a predominant substance in the CNS, has not yet been determined. To investigate the possible function of NAA as a lipid precursor [14C]-N-acetyl-L-aspartate (NAA) or [14C]-acetate (AcA) was injected intracerebrally into 8, 15- and 22-day-old rats. These time points were selected because NAA concentration and the activity of the NAA synthetizing enzyme L-aspartate-N-acetyltransferase (ANAT) were low in 8-day-old rats, intermediate in 15-day-old rats and high in 22-day-old rats. During an incubation period of 4 h the radioactive acetyl group of NAA is incorporated into the lipid fraction in amounts of 42.9 to 65.7% of recovered total radioactivity, increasing with the age of the rats. In contrast, radioactivity incorporated from AcA is constant for all three ages. With NAA as precursor only 7.2-9.4% of the recovered total radioactivity is incorporated into the protein fraction. With AcA as precursor 27.0-18.1% of recovered radioactivity is incorporated into the protein fraction, the amounts decreasing with age. Taking into account that in vivo NAA concentration in the brain is much higher than the AcA concentration, NAA is clearly the more efficient precursor for lipid synthesis than AcA. Further, we compared NAA and AcA as lipid precursors by analyzing the radioactivity in single lipid fractions, expressed as normalized specific incorporation or normalized incorporation. The measured differences between NAA and AcA in normalized specific and normalized incorporation of acetyl groups imply that NAA is not simply degraded to AcA before incorporated into lipids. We conclude that NAA is a major source of acetyl groups for lipid synthesis during rat brain development.
N-乙酰-L-天冬氨酸（NAA）是中枢神经系统中的一种主要物质，其功能尚未确定。为了研究NAA作为脂质前体的可能功能，将[14C]-N-乙酰-L-天冬氨酸（NAA）或[14C]-乙酸盐（AcA）脑内注射到8日龄、15日龄和22日龄的大鼠体内。选择这些时间点是因为8日龄大鼠的NAA浓度和NAA合成酶L-天冬氨酸-N-乙酰转移酶（ANAT）的活性较低，15日龄大鼠的处于中等水平，22日龄大鼠的较高。在4小时的孵育期内，NAA的放射性乙酰基团以回收的总放射性的42.9%至65.7%的量掺入脂质部分，并随大鼠年龄的增加而增加。相比之下，三个年龄段从AcA掺入的放射性是恒定的。以NAA作为前体时，回收的总放射性中只有7.2-9.4%掺入蛋白质部分。以AcA作为前体时，27.0-18.1%回收的放射性掺入蛋白质部分，其数量随年龄减少。考虑到脑内NAA的体内浓度远高于AcA的浓度，NAA显然是比AcA更有效的脂质合成前体。此外，我们通过分析单一脂质部分中的放射性，以标准化比掺入或标准化掺入表示，比较了NAA和AcA作为脂质前体的情况。NAA和AcA在乙酰基团的标准化比掺入和标准化掺入方面的测量差异表明，NAA在掺入脂质之前并非简单地降解为AcA。我们得出结论，NAA是大鼠脑发育过程中脂质合成乙酰基团的主要来源。
