Complete Amino Acid Sequence of a Polypeptide from Zea mays Similar to the Pathogenesis-Related-1 Family

A polypeptide serologically related to the tobacco pathogenesis-related-1 family of proteins has been purified from the root tissue of maize (Zea mays L.), and the complete amino acid sequence has been determined. The mature protein has a calculated molecular weight of 14,970 and isoelectric point of 4.2. The maize protein shows 66 to 68% amino acid identity with the tobacco pathogenesis-related-1 family and 55% identity with the tomato p14 protein.     

Novel silylated steroids as aromatase inhibitors

Androst-4-en-3-one analogs incorporating a trimethylsilyl or a trimethylsilylmethyl group at C-1, C-2 or C-19 were prepared and evaluated as inhibitors of aromatase. Only 10-[1-hydroxy-2-(trimethylsilyl)ethyl]estr-4-ene-3,17-dione inhibited human placental aromatase. Enzyme kinetic analysis revealed competitive inhibition [apparent dissociation constant (Ki) of 562 +/- 12 nM] associated with marginal time-dependent inhibition.     

Reaction of cyanide with cytochrome aa3 in isolated perfused rat head in situ.

The reaction of cyanide with cytochrome aa3 in intact mitochondria is known to differ significantly from the reaction with the isolated enzyme. To examine the cyanide reaction with cytochrome aa3 in situ, we studied the spectral characteristics and the reaction kinetics of cyanide with reduced brain cytochrome aa3 in an isolated perfused rat head preparation. Anaesthetized rats underwent bilateral carotid-arterial cannulation. The head (skull intact, muscle removed) was perfused with a crystalloid solution containing Na2S2O4, and the animal was then decapitated. By means of reflectance spectrophotometry the reaction of cyanide with cytochrome aa3 was continuously monitored with the use of the 590 nm-575 nm, 610 nm-575 nm and 590 nm-610 nm wavelength pairs. We found that: the kinetics of the absorbance change at 590 nm and 610 nm were similar, with almost identical apparent rate constants, suggesting that these spectral changes are the results of the formation of a single complex; the difference spectrum obtained on addition of cyanide to the fully reduced preparation showed a peak at 588 nm and a trough at 610 nm, consistent with spectral characteristics of the cyanide-ferrocytochrome aa3 complex in isolated enzyme and isolated mitochondria in vitro; this observation underscores the accuracy of monitoring the effects of inhibitors of mitochondrial function on cytochrome redox reactions in situ; the half-maximal (K0.5) effect was approx. 50 microM, significantly lower than that in vitro. The lower apparent K0.5 for cyanide in this preparation in situ may be due to a difference in the pH of the two systems. This approach provides the means to study the inhibitors of mitochondrial function in intact brain under a physiological environment.     

Vesicular stomatitis virus Indiana glycoprotein as a T-cell-dependent and -independent antigen.

The neutralizing immunoglobulin M (IgM) response to vesicular stomatitis virus (VSV) has been shown to be largely T-cell independent in several T-cell-deficient models of mice. By using different antigen froms of VSV, VSV antigen doses could be graded in vivo (infectious > > UV inactivated > formalin inactivated). The present study reveals a T-cell-dependent component of the neutralizing IgM response in nude mice given intravenous injections of low doses of noninfectious UV-inactivated VSV serotype Indiana (VSV-IND) only if the mice are transfused with VSV-IND-specific helper T cells. Instead, nude mice immunized with infectious VSV, which leads to greater antigen doses in vivo, were able to mount an IgM response in the absence of T cells. These results indicate that the IgM response to low doses of VSV-IND glycoprotein (G) is T-cell dependent. Nude mice immunized with infectious VSV also made a variable but low VSV-IND-neutralizing IgG response. A VSV-IND matrix (M)-specific helper T-cell line rendered this response more consistent, much higher, and longer lasting. Thus (i) VSV-G induces a mostly T-cell-independent but partially T-cell-dependent IgM (the latter can be visualized best at low doses of antigen) and (ii) the antibody response to VSV in nude mice proceeds through steps, i.e., IgM and IgG, that are dose dependent. The results suggest that the predominant role of helper T cells may be to expand and maintain the individual steps of differentiating B cells.     

Increased cell surface EGF receptor expression during the butyrate-induced differentiation of human HCT-116 colon tumor cell clones

Several clonal sublines of HCT-116 human colon adenocarcinoma cells were isolated and characterized on the basis of their growth characteristics, intrinsic enterocyte-like differentiation (as assessed by alkaline phosphatase and lactase activities), and responses to butyrate, an inducer of colon tumor cell maturation. The HCT-116 sublines were found to be heterogeneous and several phenotypically distinct clones were identified. Further characterization of these clones indicated that the effects of butyrate on cell growth, alkaline phosphatase activity, and lactase activity were distinct and separable. The growth of all of the clones were inhibited by butyrate (IC50 values varied from 0.44 to 1.5 mM), but the effects of this agent on alkaline phosphatase and lactase activities varied widely. In several sublines butyrate had no effect on either enzyme while in others one or both activities were induced. Additionally, the binding of 125I-epidermal growth factor (EGF) to cell surface receptors was found to be proportional to the expression of lactase activity in the cell. The D3 clone and other sublines with intrinsic lactase activities greater than 100 nmol/mg/min expressed a class of high-affinity EGF receptors (e.g., D3 cells had 3.48 X 10(4) EGF receptors/cell with a kd of 0.61 nM). Other clones with less lactase activity had undetectable levels of 125I-EGF binding. In clones which exhibited greater than twofold increases in lactase activity in response to butyrate, the expression of a large number of low-affinity EGF receptors was also induced. In one such clone, the P1 subline, lactase activity was increased from 70 nmol/mg/min to 230 nmol/mg/min after 96 h in 2 mM butyrate, and the expression of EGF receptors was increased from undetectable levels to 1.18 X 10(5) EGF receptors/cell (kd of 3.2 nM). Northern blot analysis indicated that the increased 125I-EGF binding after butyrate treatment may have been due, in part, to a greater than twofold accumulation of EGF receptor mRNA. In addition, the expression of the messages for transforming growth factor alpha (TGF-alpha) and transforming growth factor beta (TGF-beta) was examined in butyrate-treated cells. While TGF-alpha mRNA levels were found to correlate with EGF receptor message levels in the HCT-116 clones, TGF-beta mRNA expression was not found to correlate with the butyrate-induced growth inhibition or with increases in EGF receptor expression, alkaline phosphatase activity, or lactase activity in these cells.     

The inhibition of human neutrophil elastase and cathepsin G by peptidyl 1,2-dicarbonyl derivatives

Neutrophil elastase and cathepsin G are serine proteases that can damage connective tissue and trigger other pathological reactions. Compounds containing a peptide sequence to impart specificity and bearing an alpha-dicarbonyl unit (alpha-diketone or alpha-keto ester) at the carboxy terminus are potent inhibitors of the neutrophil serine proteases (human neutrophil elastase: R-Val-COCH3, Ki = 0.017 microM; R-Val-COOCH3, Ki = 0.002 microM; human neutrophil cathepsin G: R-Phe-COCH3, Ki = 0.8 microM; R-Phe-COOCH3, Ki = 0.44 microM; R = N-(4-[(4-chlorophenyl)sulfonylaminocarbonyl]phenylcarbonyl)+ ++ValylProlyl).     

甘南黄河流域4种典型林分土壤C、N、P化学计量特征

土壤碳（C）、氮（N）、磷（P）是参与植物光合作用和影响生态系统初级生产力的主要元素。甘南高原是黄河流域重要的生态屏障,为了解该区不同林分土壤养分状况的差异,选取该区4种典型林分：云杉林、华北落叶松林、巴山冷杉林以及岷江冷杉糙皮桦混交林为研究对象,研究土壤C、N、P化学计量特征。结果表明：（1）岷江冷杉及糙皮桦混交林土壤C、N含量最高,云杉林土壤N、P含量最低。不同林分间P含量差异显著（P<0.05）,不同土层间C、N含量差异均显著（P<0.05）。（2）云杉林土壤C ： N值显著高于其他林分,岷江冷杉及糙皮桦混交林土壤N ： P及C ： P高于其他林分。（3）海拔、土壤pH、容重与土壤含水量是影响土壤养分的重要因素。土壤C含量与N、P含量均显著相关（P<0.05）。总体来说,不同林分土壤化学计量特征具有显著差异,混交林土壤养分状况较纯林好,未来森林管理和植被建设中,可以通过选择合适的树种和提高树种多样性有效改善森林土壤质量。     

超高浓度培养基条件下酵母细胞生长及酒精生成的准稳态动力学研究

在1．5L搅拌式发酵罐中,使用葡萄糖质量浓度分别为120、200、280g／L的培养基进行酿酒酵母Saccharomyces cerevisiae连续发酵生成酒精的动力学研究。研究发现,当培养基中葡萄糖浓度为200和280g／L时,发酵液中残糖浓度、酒精浓度以及菌体生物量从小幅度波动的准稳态发展到大幅度波动的振荡状态。提出了伴有周期性振荡现象准稳态过程的概念,并针对该过程,建立了兼有底物和产物抑制的酵母细胞生长和产物酒精生成动力学模型。     

PEX16 contributions to peroxisome import and metabolism revealed by viable Arabidopsis pex16 mutants

Peroxisomes rely on peroxins(PEX proteins) for biogenesis, importing membrane and matrix proteins, and fission. PEX_16, which is implicated in peroxisomal membrane protein targeting and forming nascent peroxisomes from the endoplasmic reticulum(ER), is unusual among peroxins because it is inserted co-translationally into the ER and localizes to both ER and peroxisomal membranes. PEX_16 mutations in humans, yeast, and plants confer some common peroxisomal defects; however, apparent functional differences have impeded the development of a unified model for PEX_16 action. The only reported pex_16 mutant in plants, the Arabidopsis shrunken seed1 mutant, is inviable,complicating analysis of PEX_16 function after embryogenesis. Here, we characterized two viable Arabidopsis pex_16 alleles that accumulate negligible PEX_16 protein levels. Both mutants displayed impaired peroxisome function-slowed consumption of stored oil bodies, decreased import of matrix proteins, and increased peroxisome size. Moreover,one pex_16 allele exhibited reduced growth that could be alleviated by an external fixed carbon source, decreased responsiveness to peroxisomally processed hormone precursors, and worsened or improved peroxisome function in combination with other pex mutants. Because the mutations impact different regions of the PEX_16 gene, these viable pex_16 alleles allow assessment of the importance of Arabidopsis PEX_16 and its functional domains.