Detoxification of tetrodotoxin by thiol sinthe liver of puffer fish

河豚毒素（TTX，1）是河豚鱼体内的一种强神经毒素，其代谢途径目前还不清楚。从2000年春季采集的河豚鱼肝脏中发现一种新的天然TTX类似物4-L-半胱氨酸TTX（4-CysTTX，2）。在这份报告中，2的结构确认，和TTX与硫醇的反应进行了描述。0.4 mg）通过连续液相色谱法从200 g河豚的肝脏中分离。根据光谱数据，确定2是1的类似物，其中C4的赤道羟基被半胱氨酸的硫原子取代。2是由4，9-脱水TTX（4）与大量过量（100-500 equiv.）在pH7.0 -8.0的磷酸盐缓冲液中，于40℃反应90 min，半胱氨酸的浓度为0.001 mg/L，反应时间为90 min。其它硫醇、谷胱甘肽（GSH）、巯基乙醇（ME）和半胱氨酰甘氨酸类似地与4反应以产生在C4为1的硫取代的化合物。在具有过量得多的硫醇（超过20000当量）的条件下，在较长的反应时间内（大于8小时），ME和GSH也能与1反应，由4生成相同的衍生物。我们还证实了4-谷胱甘肽TTX先被谷氨酰转肽酶水解为4-半胱氨酰甘氨酸TTX，再被二肽酶水解为2。根据小鼠生物测定结果，口服硫醇。与Fujii等的结果相反，TTX不能有效降低TTX的毒性。

Metabolic pathway of tetrodotoxin (TTX, 1), a potent neurotoxin in puffer fish, has not been clarified yet, for puffer fish and also for human. We found a new natural analog of TTX, 4-L-cycteineTTX (4-CysTTX,2) from the liver of the puffer fish, Fugu pardalis, collected in spring in 2000. In this report, structural confirmation of 2, and the reaction of TTXs with thiols are described.2 (ca. 0.4 mg) was isolated from 200 g of liver of the puffer fish by sequential liquid chromatography. Based on the spectroscopic data, 2 was determined as an analog of 1 of which equatorial hydroxyl group at C4 was substituted by sulfur atom of cysteine. Configuration of cysteine was confirmed to be L by using Marfey reagent for cysteine obtained from 2 by I_2 oxidation.2 was produced by the reaction of 4,9-anhydroTTX (4) and large excess (100-500 equiv.) of cysteine in phosphate buffer (pH 7.0-8.0) at 40℃ for 90 mm. It was pH dependent reaction. Other thiols, glutathione (GSH), mercaptoethanol (ME), and cysteinyl glycine were similarly reacted with 4 to produce sulfur substituted compounds at C4 of 1. On the condition with much more excess of thiols (more than 20000 equiv.) and for longer reaction time (longer than 8 hr), ME and GSH were also reacted with 1 to produce the same derivatives from 4.We also confirmed that 4-glutathioneTTX was hydrolyzed by glutamyltranspeptidase to 4-cysteinylglysineTTX, and then to 2 by the dipeptidase. According to the results of mouse bioassay, oral administration of thiols. with TTX was not effective to decrease the toxicity of TTX, contrary to the results by Fujii et al.