Expression of the quinolinate-synthesizing enzyme gene in the brain of the epilepsy-prone El mice

喹啉酸（QUIN）是神经递质l -谷氨酸和l -天冬氨酸的结构类似物，因此，当它在大脑中含量丰富时，可以作为兴奋毒素。本研究的目的是探讨QUIN在癫痫性疾病发病机制中的可能参与。结果发现，在癫痫易感El小鼠的大脑中，3-羟基苯甲酸3,4-双加氧酶（3- haoase）的活性非常高。相比之下，El小鼠和对照组小鼠的大脑中奎恩降解酶——奎恩磷酸转氨酶的活性没有显著差异。El小鼠大脑皮层中QUIN的含量是对照小鼠的两倍。综上所述，上述结果提示，致痫小鼠大脑中高浓度的QUIN可能是由于3-HAOase基因的异常表达所致。为了估计基因的表达模式，我们试图克隆它的c-DNA。首先，从大鼠肝脏中纯化3-HAOase为单一蛋白。然后对其n端氨基酸进行测序。根据氨基酸序列合成DNA寡核苷酸。用寡核苷酸作为探针克隆了该酶的c-DNA。

Quinolinic acid (QUIN) is a structural analog of neurotransmitters, L-glutamate and L-aspartate and, hence, may act as an excitotoxin when it is abundant in the brain. The purpose of this study is to examine the possible involvement of QUIN in the pathogenesis of the epileptic diseases. It was found that the activity of 3-hydroxyanthranilate 3,4-dioxygenase (3-HAOase), a QUIN-synthesizing enzymes, was very high in the brain of the epilepsy-prone El mice. In contrast, there was no significant difference in the activity of the QUIN-degradating enzymes, QUIN-phophoribosystransferase, between the brain of the El mice and that of the control mice. The QUIN content in the cerebral cortex of the El mice was twice as high as that of the control mice. These results, in together, indicate that high concentration of QUIN in the brain of the epileptogenic mice may be due to abnormal expression of the gene for 3-HAOase. In order to estimate the mode of expression of the gene we then tried to clone its c-DNA.At first, 3-HAOase was purified from the rat liver to a single protein. Its N-terminal amino acids were then sequenced. The DNA oligonucleotides were synthesized in referring to the amino acid sequence. The c-DNA for the enzyme was cloned using the oligonucleotides as probes.