Peptidyltransferase center of ribosomes: On the mechanism of action of alkaloid lycorine

The molecular mechanism of action of the alkaloid lycorine has been revised. According to our results, lycorine inhibits the binding of CACCA-Leu←Ac to the donor site of the peptidyltranferase center of wheat-germ ribosomes, whereas the transpeptidation reaction in the system with the minimal model donor is not inhibited. The equilibrium constant of CACCA-Leu←Ac to the donor site of 80 S ribosomes is measured.     

Alkaloid biosynthesis in somatic hybrids of Duboisia leichhardtii F. Muell. and Nicotiana tabacum L.

Somatic hybrids of Duboisia leichhardtii and Nicotiana tabacum were obtained by electrofusion followed by individual cloning. The hybrid nature of the cloned cells and regenerated shoots was confirmed by cytological investigation and ribosomal-DNA analysis, respectively. The hybrid plantlets predominantly produced nicotine, while Duboisia plantlets produced both tropane and nicotine alkaloids. Activities involved in tropane-alkaloid biosynthesis were examined in a series of precursor-feeding experiments. The presence in the hybrid plants of activities responsible for the reduction of tropinone, the hydroxylation and epoxidation of hyoscyamine, and the conversion of nicotine to nornicotine demonstrated the presence of the Duboisia genes for these enzyme activities.We thank Mr. T. Shikanai, Kyoto University, for the preparation of rice rRNA. We also appreciate Dr. J.H. Fitchen, Kyoto University, for critical discussion and English correction.     

植物生物碱代谢生物学研究进展

 目前,植物生物碱作为植物的化学防御武器,在植物的生态适应过程中发挥积极作用的观点已得到了普遍的接受。生物碱代谢生物学的研究近年来取得了长足的进步,主要集中在生物碱合成和贮存部位、转运途径、代谢调控因子、生物合成途径和关键酶及其编码基因等方面,现就这方面的进展作一简要综述,并提出了该领域尚存在的问题和前景展望。     

光照对水母雪莲愈伤组织合成生物碱的影响

以水母雪莲（Saussurea medusa Maxin.)无菌幼苗的根作外植体,诱导获得的愈伤组织为材料,研究光照对生物碱合成的影响。结果表明：尽管在水母雪莲的愈伤组织培养物中,总生物碱的含量比原植株中的含量低,但其组成成分比原植物丰富。并且秋水仙碱的含量也比原植物高,尤其是在光照培养的愈伤组织中秋水仙碱大大增加。     

植物细胞生物碱跨膜传递模型研究(II)-膜电位影响下的饱和特性模型

在中性生物碱饱和特性模型的基础上,引入膜电位的影响,考虑生物碱阳离子通量对总生物碱扩散通量的影响,从而导出膜电位影响的饱和特性模型。将模型在特定参数下积分,对实验结果进行数值模拟,结果表明,所建模型可很好描述各种生物碱（高ｐＫａ值和低ｐＫａ值生物碱）的跨膜传递过程,为建立描述生物碱跨膜传递过程的普适性模型提供了理论基础     

Influence of exogenous hormones on the growth and secondary metabolite formation in transformed root cultures

Transformed organ cultures formed following transformation of plant tissues with Agrobacterium species owe their phenotypes to alterations in hormone metabolism. Exogenously supplied hormones have been used to probe the relationship between the growth and morphology of transformed root cultures of a number of species and their ability to accumulate secondary products. Auxins in the presence of low levels of kinetin induce the rapid disorganisation of transformed roots of Nicotiana rustica ultimately toform suspension cultures of transformed cells and this process is associated with a decrease in nicotine content of the cells. This is related to cells in the culture losing competence in alkaloid biosynthesis. In contrast, exogenously supplied GA₃ enhanced branching in two transformed root clones of the tropane-alkaloid producing species, Brugmansia candida and so enhanced their typical hairy root phenotype. This growth substance had the effect of reducing the overall alkaloid accumulation but in one case significantly altered the relative concentrations of different tropine esters.In transformed roots of Cucumis sativus, the phenotype of the roots is influenced by the expression of auxin synthesis genes on T_R-DNA resulting in roots with two distinct morphologies. The pattern of expression of the enzyme ascorbate oxidase in populations of control roots of different morphologies is described. The significance of these phenotypic variations on the utility of transformed root cultures for the study of secondary metabolic pathways will be discussed.Abbreviations AO ascorbate oxidase - DW dry weight - FW fresh weight - GA₃ gibberellic acid     

Staurosporine, K-252a, and K-252b Stabilize Calcium Homeostasis and Promote Survival of CNS Neurons in the Absence of Glucose

Abstract: Staurosporine, K-252a, and the 9-carboxylic related compound K-2525 are low-molecular-weight alkaloids from microbial origin that at high concentrations are kinase inhibitors and can antagonize the effects of neuronal growth factors. Paradoxically, we have found that very low concentrations of these agents (10 f M -10 n M ) prolong the survival of hippocampal, septal, and cortical neurons deprived of glucose. These agents did not prevent the depletion of ATP caused by glucose deprivation. The large elevation of intracellular calcium levels that normally mediates glucose deprivation-induced damage was attenuated by Staurosporine, K-252a, and K-252b. Western blot analysis using antiphosphotyrosine antibody showed that Staurosporine and the K-252 compounds (10–100 p M ) stimulated tyrosine phosphorylation of several different proteins. The tyrosine kinase inhibitor genistein significantly reduced the protective effect of Staurosporine and the K-252 compounds, indicating that tyrosine phosphorylation was required for neuroprotection by these compounds. Taken together, the data demonstrate that low concentrations of Staurosporine and the K-252 compounds can stabilize calcium homeostasis, possibly by a mechanism involving activation of receptor tyrosine kinase transduction pathways.     

串叶松香草的药用成分分析

本文对串叶松香草的药用成分作了定性分析,并对松香草中的核黄素和单宁作了较深入的探讨,结合用该草作的抗疲劳试验和各地的饲喂实践,可以看出,串叶松香草是一种既有高营养价值,又有多种药物疗效的优质饲草。     

Comment on Amézquita et al. (2017) “Conspicuousness,color resemblance,and toxicity in geographically diverging mimicry: The pan‐Amazonian frog Allobates femoralis”

Amézquita et al. (2017) recently concluded that species of the Allobates femoralis group are toxic to mice at levels equivalent to syntopic alkaloid‐containing poison frogs, which they attributed to the presence of alkaloids in skin secretions. However, the chemical composition of skin secretions was not analyzed, and here we present additional data supporting the absence of alkaloids in skin secretions of the Allobates femoralis group. Instead, we suggest the observed toxicity was caused by the anesthetic benzocaine, which was applied to the buccal cavity to euthanize frogs prior to skin removal. We show that orally administered benzocaine is rapidly incorporated into the skin of species that sequester and do not sequester alkaloids, which casts doubt on the conclusion that Allobates femoralis group skin secretions are toxic and makes the results of experiments with alkaloid‐containing species of Adelphobates and Ameerega uninterpretable. To prevent experimental errors and misinterpretations in studies of amphibian chemical defense, we encourage researchers to test the chemical composition of samples prior to experimentation, include all necessary controls to detect false positives, conduct small pilot studies for new methods, and consider the limitations of particular methods and their ability to address the intended research questions.