除虫菊的染色体数目及其核型

除虫菊(Pyrethrum cinerariifolium Trev.)为菊科小黄菊属多年生宿根草本植物。以花或全草入药。除虫菊的主要有效成分为除虫菊酯和瓜叶除虫菊酯,可用于加工成各种制剂作杀虫剂原料,用以防治日常虫豸(蚊、蝇、虱等)和农业害虫,且对人     

一种纯化细菌有机磷水解酶的简便方法

Cibacron blue T_3GA与溴化氰活化的Sepharose 4B偶联后,产生一种能有效地分离有机磷水解酶的吸附剂。用0.15mol/L MgCl_2溶液从黄杆菌P3—2细胞抽提出的粗酶液通过柱层析分离,即可得到纯化8倍、酶活性回收率为269.4％的纯酶制品。该酶制品用凝胶电泳测是均一的。     

A threshold result for an epidemiological model

A threshold parameter R ₀ is identified for an SIRS epidemiological model which has nonlinear incidence and a distributed delay for transfer out of the removed class. For R ₀ < 1, the disease free equilibrium is proved to be the global attractor for all solutions.Research supplied in part by NSERC A-8965     

Molecular cloning of the cDNA for the catalytic subunit of human DNA polymerase delta.

The cDNA of human DNA polymerase delta was cloned. The cDNA had a length of 3.5 kb and encoded a protein of 1107 amino acid residues with a calculated molecular mass of 124 kDa. Northern blot analysis showed that the cDNA hybridized to a mRNA of 3.4 kb. Monoclonal and polyclonal antibodies to the C-terminal 20 residues specifically immunoblotted the human pol delta catalytic polypeptide. A multiple sequence alignment was constructed. This showed that human pol delta is closely related to yeast pol delta and the herpes virus DNA polymerases. The levels of pol delta message were found to be induced concomitantly with DNA pol delta activity and DNA synthesis in serum restimulated proliferating IMR90 cultured cells. The human pol delta gene was localized to chromosome 19 by Southern blotting of EcoRI digested DNA from a panel of rodent/human cell hybrids.     

电损毁海马CA3区及连合前穹窿对大鼠血浆胰岛素水平...

Bilateral electrical lesioning of the hippocampal CA3 region (HCA3-EL) or anterior commissura hippocampi (ACHF-EL) caused marked elevations in plasma basal levels of insulin. 2 weeks later, fasting blood glucose levels were also augmented with decreased glucose tolerance. In contrast, the secretory response of pancreatic B cells to glucose stimulation was markedly enhanced. Following intravenous glucose tolerance test (IVGTT), the relative amounts of glucagon-like and insulin-like immunoreactants were reduced in the pancreatic islets of both HCA3-EL and ACHF-EL rats in comparison with the controls. In the HCA3-EL group, the relative amounts of somatostatin-like immunoreactants and gross numbers of such immunostained cells in islets were also decreased as compared with the control. No difference was seen in pancreatic-polypeptide-like immunoreactivities as assessed by immunohistochemistry plus microphotometry method. The above results suggest strongly that HCA3 and ACHF exert a tonic inhibitory action on the insulin secretion in the rat.     

Replacement of lysine-181 by aspartic acid in the third transmembrane region of endothelin type B receptor reduces its affinity to endothelin peptides and sarafotoxin 6c without affecting G protein coupling.

A conserved aspartic acid residue in the third transmembrane region of many of the G protein-coupled receptors has been shown to play a role in ligand binding. In the case of endothelin receptors, however, a lysine residue replaces this conserved aspartic acid residue. To access the importance of this residue in ligand binding, we have replaced it with an aspartic acid in the rat endothelin type B (ETb) receptor by PCR mediated mutagenesis. The binding characteristics and functional properties of both the wild type and mutant receptors were determined in COS-7 cells transiently expressing the cloned receptor cDNAs. Using 125I-ET-1 as the radioactive peptide ligand in displacement binding studies, the wild type receptor displayed a typical non-isopeptide-selective binding profile with similar IC50 values (0.2-0.6 nM) for all three endothelin peptides (ET-1, ET-2, and ET-3) and sarafotoxin 6c (SRTX 6c). Interestingly, the mutant receptor showed an increase in IC50 values for ET-1 (5 nM), ET-2 (27 nM), and ET-3 (127 nM) but displayed a much larger increase in IC50 value for SRTX 6c (> 10 uM). The lysine mutant receptor still elicited full inositol phosphate (IP) turnover responses in the presence of saturating concentrations of endothelins (10 nM of ET-1, 100 nM of ET-2, or 1 uM of ET-3), indicating that the mutation (K181D) did not affect the coupling of mutant receptor to the appropriate G protein. These results demonstrate that lysine-181 on the receptor is important for binding ET peptides; however, it is required for binding the ETb selective agonist-SRTX 6c.     

Water Transport across Maize Roots : Simultaneous Measurement of Flows at the Cell and Root Level by Double Pressure Probe Technique

A double pressure probe technique was used to measure simultaneously water flows and hydraulic parameters of individual cells and of excised roots of young seedlings of maize (Zea mays L.) in osmotic experiments. By following initial flows of water at the cell and root level and by estimating the profiles of driving forces (water potentials) across the root, the hydraulic conductivity of individual cell layers was evaluated. Since the hydraulic conductivity of the cell-to-cell path was determined separately, the hydraulic conductivity of the cell wall material could be evaluated as well (Lp_cw = 0.3 to 6.10⁻⁹ per meter per second per megapascal). Although, for radial water flow across the cortex and rhizodermis, the apoplasmic path was predominant, the contribution of the hydraulic conductance of the cell-to-cell path to the overall conductance increased significantly from the first layer of the cortex toward the inner layers from 2% to 23%. This change was mainly due to an increase of the hydraulic conductivity of the cell membranes which was Lp = 1.9.10⁻⁷ per meter per second per megapascal in the first layer and Lp = 14 to 9.10⁻⁷ per meter per second per megapascal in the inner layers of the cortex. The hydraulic conductivity of entire roots depended on whether hydrostatic or osmotic forces were used to induce water flows. Hydrostatic Lp_r was 1.2 to 2.3.10⁻⁷ per meter per second per megapascal and osmotic Lp_r = 1.6 to 2.8.10⁻⁸ per meter per second per megapascal. The apparent reflection coefficients of root cells (σ_s) of nonpermeating solutes (KCI, PEG 6000) decreased from values close to unity in the rhizodermis to about 0.7 to 0.8 in the cortex. In all cases, however, σ_s was significantly larger than the reflection coefficient of entire roots (σ_sr). For KCI and PEG 6000, σ_sr was 0.53 and 0.64, respectively. The results are discussed in terms of a composite membrane model of the root.     

Activation of Plasma Membrane NADH Oxidase Activity by Products of Phospholipase A

An auxin-stimulated NADH oxidase activity (NADH oxidase I) of plasma membrane vesicles, highly purified by aqueous two-phase partition from soybean (Glycine max Merr.) hypocotyls was activated by lysophospholipids and fatty acids, both products of phospholipase A action. The activation of NADH oxidase activity occurred slowly, suggesting a mechanism whereby the lipids acted to stabilize the enzyme in a more active configuration. In contrast to activation by lipids, the activation by auxin was rapid. The average K_m of the NADH oxidase after activation by lipids was four- to fivefold less than the K_m before activation. The V_max was unchanged by activation. The increases occurred in the presence of detergent and thus were not a result of exposure of latent active sites. Also, the activation did not result from activation of a peroxidase or lipoxygenase. Fatty acid esters, where growth promoting effects have been reported, also activated the auxin-stimulated oxidase. However, the auxin stimulation of NADH oxidase I did not appear to be obligatorily mediated by phospholipase A, nor did inhibitors of phospholipase A₂ block the stimulation of the oxidase by auxins.