Department of Pharmacology and Therapeutic Innovation, Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
Department of Pharmacology and Therapeutic Innovation, Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
Peptides. 2018 Mar;101:60-68. doi: 10.1016/j.peptides.2017.12.026. Epub 2017 Dec 28.
Kyotorphin (KTP; L-tyrosyl-l-arginine), an opioid-like analgesic discovered in the bovine brain, is potentially a neuromodulator because of its localization in synaptosomes, the existence of a specific KTP receptor, and the presence of its biosynthetic enzyme in the brain. KTP is formed in the brain from its constituent amino acids, L-tyrosine and L-arginine, by an enzyme termed KTP synthetase. However, the latter has never been identified. We aimed to test the hypothesis that tyrosyl-tRNA synthetase (TyrRS) is also KTP synthetase. We found that recombinant hTyrRS synthesizes KTP from tyrosine, arginine, and ATP, with Km = 1400 μM and 200 μM for arginine and tyrosine, respectively. TyrRS knockdown of PC12 cells with a small interfering RNA (siRNA) in the presence of 1.6 mM tyrosine, arginine, proline, or tryptophan significantly reduced the level of KTP, but not those of tyrosine-tyrosine, tyrosine-proline, or tyrosine-tryptophan. siRNA treatment did not affect cell survival or proliferation. In mice, TyrRS levels were found to be greater in the midbrain and medulla oblongata than in other brain regions. When arginine was administered 2 h prior to brain dissection, the KTP levels in these regions plus olfactory bulb significantly increased, although basal brain KTP levels remained relatively even. Our conclusion is further supported by a positive correlation across brain regions between TyrRS expression and arginine-accelerated KTP production.
脑啡肽（KTP；L-酪氨酸-L-精氨酸）是一种在牛脑中发现的类阿片样镇痛剂，由于其在突触小体中的定位、存在特异性 KTP 受体以及其生物合成酶在脑中的存在，因此它可能是一种神经调节剂。KTP 是由其组成氨基酸 L-酪氨酸和 L-精氨酸在脑内由一种称为 KTP 合成酶的酶形成的。然而，后者从未被鉴定过。我们的目的是检验酪氨酸 tRNA 合成酶（TyrRS）也是 KTP 合成酶的假设。我们发现重组 hTyrRS 可以从酪氨酸、精氨酸和 ATP 合成 KTP，Km 值分别为 1400 μM 和 200 μM。在存在 1.6 mM 酪氨酸、精氨酸、脯氨酸或色氨酸的情况下，用小干扰 RNA（siRNA）敲低 PC12 细胞中的 TyrRS，可显著降低 KTP 的水平，但不降低酪氨酸-酪氨酸、酪氨酸-脯氨酸或酪氨酸-色氨酸的水平。siRNA 处理不影响细胞存活或增殖。在小鼠中，中脑和延髓的 TyrRS 水平高于其他脑区。当在脑解剖前 2 小时给予精氨酸时，这些区域加上嗅球的 KTP 水平显著增加，尽管基础脑 KTP 水平仍相对均匀。我们的结论还得到了脑区之间 TyrRS 表达与精氨酸加速 KTP 产生之间正相关的进一步支持。
