Blakely R D, Robinson M B, Thompson R C, Coyle J T
Division of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
J Neurochem. 1988 Apr;50(4):1200-9. doi: 10.1111/j.1471-4159.1988.tb10593.x.
N-Acetylated-alpha-linked acidic dipeptidase (NAALADase) is a Cl- dependent, membrane bound, metallopeptidase that cleaves the endogenous neuropeptide N-acetyl-L-aspartyl-L-glutamate (NAAG) in vitro. To examine the pattern of NAALADase expression in the CNS, subcellular, regional, and developmental studies were conducted. Subcellular fractionation of lysed synaptosomal membranes revealed a substantial enrichment of the peptidase in synaptic plasma membranes as compared to mitochondrial or myelin subfractions. Regional studies reveal an apparent restriction of peptidase activity to kidney and brain. A threefold variation in specific activity was observed among brain regions, with highest specific activity in the cerebellum and lowest in telencephalic structures, a pattern that does not, in general, correlate with NAAG levels. Ontogenetic studies demonstrate a region-dependent, postnatal pattern of expression of NAALADase activity, with adult levels attained earliest in brainstem, as was previously reported for NAAG. Postnatal NAALADase expression would not appear to support a role for the peptidase in constitutive protein processing, but rather suggests that NAALADase may play a role in synaptic peptide degradation. Glutamate (Glu) excised from NAAG by NAALADase could be transported efficiently by uptake processes. Lesion studies, however, do not support a close structural association between NAALADase activity and the corticostriatal sodium-dependent, high-affinity, Glu uptake system. Similar to in vitro data documenting the route of NAAG degradation by NAALADase, after intrastriatal injection, NAAG was rapidly cleaved to two major products, N-acetyl-aspartate and Glu, with a t1/2 of approximately 10 min. Thus, the route of in vivo catabolism of NAAG parallels results from studies on NAALADase activity in vitro. These results are consistent with a role of NAALADase in the synaptic processing of NAAG. However, certain discrepancies in the regional and ontogenetic profiles of NAAG and NAALADase suggest that this relationship is not an exclusive one and may reflect a role for NAALADase on additional N-acetylated acidic peptides in vivo.
N-乙酰化-α-连接酸性二肽酶（NAALADase）是一种依赖氯离子、与膜结合的金属肽酶，在体外可裂解内源性神经肽N-乙酰-L-天冬氨酰-L-谷氨酸（NAAG）。为研究NAALADase在中枢神经系统中的表达模式，进行了亚细胞、区域和发育方面的研究。对裂解的突触体膜进行亚细胞分级分离显示，与线粒体或髓磷脂亚级分相比，该肽酶在突触质膜中大量富集。区域研究表明，肽酶活性明显局限于肾脏和大脑。在脑区之间观察到比活性有三倍的差异，小脑的比活性最高，端脑结构中的比活性最低，一般而言，这种模式与NAAG水平不相关。个体发育研究表明，NAALADase活性的表达呈区域依赖性的出生后模式，脑干最早达到成年水平，这与之前报道的NAAG情况相同。出生后NAALADase的表达似乎不支持该肽酶在组成性蛋白质加工中发挥作用，而是表明NAALADase可能在突触肽降解中起作用。由NAALADase从NAAG中切除的谷氨酸（Glu）可通过摄取过程有效转运。然而，损伤研究不支持NAALADase活性与皮质纹状体钠依赖性、高亲和力Glu摄取系统之间存在紧密的结构关联。与记录NAALADase降解NAAG途径的体外数据相似，纹状体内注射后，NAAG迅速裂解为两种主要产物，N-乙酰天冬氨酸和Glu，半衰期约为10分钟。因此，NAAG的体内分解代谢途径与NAALADase活性的体外研究结果相似。这些结果与NAALADase在NAAG的突触加工中的作用一致。然而，NAAG和NAALADase在区域和个体发育分布上的某些差异表明，这种关系并非唯一的，可能反映了NAALADase在体内对其他N-乙酰化酸性肽的作用。
