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

喹啉酸(Quin)是一种结构类似的神经递质，L谷氨酸和L天冬氨酸，因此，当它在大脑中含量丰富时，可能起到兴奋毒素的作用。本研究的目的是探讨Quin在癫痫发病机制中的可能作用。发现癫痫易感小鼠脑内3-羟基邻氨基苯甲酸双加氧酶(3-HAOase)活性很高。相比之下，EL组小鼠大脑中Quin降解酶Quin-PhoporiBosystrferase的活性与对照组小鼠之间没有显著差异。EL组小鼠大脑皮质中的奎宁含量是对照组的两倍。这些结果提示致痫小鼠脑内奎宁浓度升高可能是由于3-羟基苯氧酶基因表达异常所致。为了推测该基因的表达模式，我们尝试克隆了该基因的c-DNA。首先，从大鼠肝脏中纯化了3-HAOase，使其成为单一蛋白。对其N端氨基酸进行了测序。参照氨基酸序列合成DNA寡核苷酸。以寡核苷酸为探针，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.