O-methylation of dopamine-0-sulfates with cathechol-0-methyltransferase

[²H₂]-dopamine-3-0-sulfate(DM-3-0-S) and [²H₂]-dopamine-4-0-sulfate (DM-4-0-S) were synthesized to investigate the possibility of their being substrates for catechol-0-methyltransferase (COMT). [²H₅]-3-0-methyldopamine (3-0-Me-DM) and [²H₅]-4-0-methyldopamine (4-0-Me-DM) were also synthesized as internal standards for the determination of enzymatic products by gas chromatography-mass spectrometry (GC-MS). [²H₂]-DM-3-0-S or [²H₂]-DM-4-0-S was incubated at 37° for 60 min in the presence of S-adenosyl-L-methionine with a crude enzyme preparation obtained from rat liver homogenate. The incubation mixture was treated with 0.5N HCl at 100°C for 1h to hydrolyze the remaining sulfate moiety. The reaction products were extracted with an Amberlite XAD-4, derivatized with pentafluoropropionic anhydride and determined by GC-MS. When [²H₂]-DM-3-0-S was used as a substrate, [²H₂]-3-0-Me-DM was found to be a major product accompanied by [²H₂]-4-0-Me-DM as a minor product. The ratio of [²H₂]-3-0-Me-DM to [²H₂]-4-0-Me-DM was found to be 26:1, while the ratio was 5.4:1 when [²H₂]-dopamine was used as a substrate. When [²H₂]-DM-4-0-S served as a substrate, [²H₂]-3-0-Me-DM was preferentially produced without detectable formation of [²H₂]-4-0-Me-DM.     

Modulation of muscarinic receptor-mediated adenylate cyclase and phospholipase C responses in rat retina

1. Agonist activation of rat retina muscarinic receptors results in suppression of cyclic AMP (cAMP) generation and enhanced phosphoinositide hydrolysis. 2. Pharmacological manipulations that elevate cAMP or stable analogues of cAMP attenuate the acetylcholine (ACh)-induced enhancement of phosphoinositide hydrolysis. We postulate that cross-talk between adenylate cyclase and phospholipase C signal transducing systems probably exists in rat retina, as has been described for other systems. 3. Intraocular administration of pertussis toxin attenuated the response of both adenylate cyclase and phospholipase C to muscarinic stimulation, suggesting that some retinal muscarinic receptors are apparently coupled to their effector systems via pertussis toxin sensitive G proteins.     

苦瓜提取物抗病毒作用及其有效成份的研究

本实验发现,小鼠皮下感染乙型脑炎病毒前腹腔注射苦瓜提取物(简称E.M.c.)有显著的保护作用,其保护率平均为66％;以E.M.c.静脉注射家兔后2小时,血清中的干扰素达高峰,其干扰素为I型干扰素;E.M.c.对小鼠NK细胞有明显的激活作用;经鉴定,E.M.c.中的有效成份主要是dsRNA,此外,还含有多糖类物质。     

玉米原生质体超低温保存后芽和根的分化

植物细胞的超低温保存,已逐步发展成为一个有效的种质保存方法。近年来,随着原生质体再生植株种类的不断增多,禾谷类的主要农作物比如水稻、玉米、小麦等     

Enzyme–substrate interaction and characterization of a 2,3-dihydroxybiphenyl 1,2-dioxygenase from Dyella ginsengisoli LA-4

A bphC gene (915 bp) encoding 2,3-dihydroxybiphenyl 1,2-dioxygenase (BphC) was amplified by PCR from Dyella ginsengisoli LA-4, which was heterologously expressed in Escherichia coli . The purified His-Tag BphC was able to catalyze the meta -cleavage reaction of the dihydroxylated aromatic rings. According to the specificity constant ( K _cat/ K _m) of BphC_LA-4, the specificity of BphC_LA-4 was determined in the following order: 2,3-dihydroxybiphenyl>3-methylcatechol>catechol>4-chlorocatechol>4-methylcatechol. The experimental data were consistent with the prediction of enzyme–substrate complexes. The highest specific activity of BphC_LA-4 was 118.3 U mg⁻¹ for 2,3-dihydroxybiphenyl.     

Biocatalytic Production of Acyclic Bis[bibenzyls] from Dihydroresveratrol by Crude Momordica charantia Peroxidase

Biotransformation of dihydroresveratrol by crude Momordica charantia peroxidase provided six new acyclic bis[bibenzyls] 1 – 6 . Their structures were established on the basis of NMR and MS analyses as C? C, C? O? C, and C? CH₂? C dimers of dihydroresveratrol. Compounds 1 – 6 were tested for antiproliferative activity against human prostate cancer PC3 cell line in vitro, and 2 and 6 were found to be more potent than the parent compound.     

Abscisic acid pretreatment enhances salt tolerance of rice seedlings: Proteomic evidence

Enhanced salt tolerance of rice seedlings by abscisic acid (ABA) pretreatment was observed from phenotypic and physiological analyses. Total proteins from rice roots treated with ABA plus subsequent salt stress were analyzed by using proteomics method. Results showed that, 40 protein spots were uniquely upregulated in the seedlings under the condition of ABA pretreatment plus subsequent salt stress, whereas only 16 under the condition of salt treatment. About 78% (31 spots) of the 40 protein spots were only upregulated in the presence of the subsequent salt stress, indicating that plants might have an economical strategy to prevent energy loss under a false alarm. The results also showed that more enzymes involved in energy metabolism, defense, primary metabolism, etc. were upregulated uniquely in ABA-pretreated rice seedlings, suggesting more abundant energy supply, more active anabolism (nitrogen, nucleotide acid, carbohydrate, etc), and more comprehensive defense systems in ABA-pretreated seedlings than in salt stressed ones.