Blom J F, Robinson J A, Jüttner F
Limnologische Station, Institut für Pflanzenbiologie, Universität Zürich, Seestr. 187, 8802 Kilchberg, Switzerland.
Toxicon. 2001 Dec;39(12):1923-32. doi: 10.1016/s0041-0101(01)00178-7.
Planktothrix rubescens, the dominant cyanobacterium in Lake Zürich, is generally considered to be toxic to zooplankton. The major toxin was determined by NMR spectroscopy and chemical analysis to be [D-Asp(3),(E)-Dhb(7)]microcystin-RR. The compound was isolated in high purity, and its 24-h acute grazer toxicity was compared with microcystin-LR, microcystin-RR, microcystin-YR, and nodularin using a Thamnocephalus platyurus bioassay. Based on LC(50) values [D-Asp(3),(E)-Dhb(7)]microcystin-RR was the most toxic microcystin tested. Nodularin was slightly more toxic under the conditions of the assay. The large number of individuals available for the grazer bioassay allowed the determination of dose-response curves of the different microcystins. These curves showed marked differences in their steepness. Microcystin-RR, which had nearly the same LC(50) as microcystin-LR and microcystin-YR, exhibited a very flat dose-response curve. This flat curve indicates that, for some individuals, lower concentrations of this microcystin are much more toxic than are the other two microcystins. Mortality of 100% requires much higher concentrations of microcystin-RR, indicating the resistance of some animals to the toxin. The purified [D-Asp(3),(E)-Dhb(7)]microcystin-RR exhibited a higher molar absorption coefficient determined by quantitative amino acid analysis than the coefficients generally used for other microcystins. This observation has consequences for the risk assessment for microcystins and makes a structural determination of microcystins an absolute requirement. The presence of the dehydrobutyrine residue may be the reason for the higher specific toxicity of [D-Asp(3),(E)-Dhb(7)]microcystin-RR when compared to the N-methyldehydroalanine-containing microcystins.
鲁氏平裂藻是苏黎世湖中的优势蓝藻，通常被认为对浮游动物有毒。通过核磁共振光谱和化学分析确定主要毒素为[D-天冬氨酸(3),(E)-脱氢丁酸(7)]微囊藻毒素-RR。该化合物被高纯度分离，并使用扁头新糠虾生物测定法将其24小时急性食草动物毒性与微囊藻毒素-LR、微囊藻毒素-RR、微囊藻毒素-YR和节球藻毒素进行比较。基于半数致死浓度(LC50)值，[D-天冬氨酸(3),(E)-脱氢丁酸(7)]微囊藻毒素-RR是所测试微囊藻毒素中毒性最强的。在该测定条件下，节球藻毒素的毒性略高。大量可用于食草动物生物测定的个体使得能够确定不同微囊藻毒素的剂量反应曲线。这些曲线在陡峭程度上显示出明显差异。微囊藻毒素-RR的半数致死浓度与微囊藻毒素-LR和微囊藻毒素-YR几乎相同，但其剂量反应曲线非常平缓。这条平缓的曲线表明，对于一些个体来说，较低浓度的这种微囊藻毒素比其他两种微囊藻毒素毒性大得多。100%的死亡率需要更高浓度的微囊藻毒素-RR，这表明一些动物对该毒素具有抗性。通过定量氨基酸分析测定，纯化的[D-天冬氨酸(3),(E)-脱氢丁酸(7)]微囊藻毒素-RR表现出比其他微囊藻毒素通常使用的系数更高的摩尔吸收系数。这一观察结果对微囊藻毒素的风险评估有影响，并使得对微囊藻毒素进行结构测定成为绝对必要。与含N-甲基脱氢丙氨酸的微囊藻毒素相比，脱氢丁酸残基的存在可能是[D-天冬氨酸(3),(E)-脱氢丁酸(7)]微囊藻毒素-RR具有更高比毒性的原因。
