Evidence that guanine-nucleotide binding regulatory proteins couple cell-surface receptors to the breakdown of inositol-containing lipids during T-lymphocyte mitogenesis

We have studied the role of guanine-nucleotide binding regulatory proteins (G proteins) in the stimulation of inositol lipid breakdown during mitogenic activation of normal human T lymphocytes. The effect of the mitogen phytohemagglutinin (PHA) was compared with the action of two G-protein activators, fluoroaluminate (AlF4-) and guanosine-5'-O-thiotriphosphate (GTP gamma S). PHA and AlF4- stimulated the breakdown of inositol lipids via both the phospholipase A and C pathways when added to intact lymphocytes. PHA, AlF4- and GTP gamma S also triggered both these pathways when added to permeable lymphocytes. The magnitude of the response obtained with AlF4- and GTP gamma S was about four-fold less than with PHA. This difference was attributable to increases in cAMP elicited by AlF4- and GTP gamma S which inhibited the phospholipase pathways. AlF4-, GTP gamma S, and PHA all stimulated the phosphorylation of a 42 kDa protein on tyrosine residues. We propose a model for the early steps following mitogen binding, including sequential activation of a G protein, phospholipase C, protein kinase C and a tyrosine protein kinase. A parallel pathway involving G protein mediated activation of phospholipase A is also implicated.     

田螺科五种螺的核型研究

以早期胚胎细胞为材料,用火焰干燥法制片,对分布于我国湖北省武汉市近郊的常见田螺科(Viviparidae)五种螺的核型进行了分析。结果:两种圆田螺的染色体数和国外报道的同一属的种类的一致。而三种环棱螺的染色体数,则较国外报道的另两种的少得多。在铜锈环棱螺的核型中,其m组的第一对和sm组的第四对染色体上,具有明显的随体,出现频率甚高。     

Phytohemagglutinin treatment of T lymphocytes stimulates rapid increases in activity of both particulate and cytosolic protein kinase C

We have measured the activity of protein kinase C in particulate and cytosolic fractions prepared from lymphocytes following stimulation with phytohemagglutinin. Activity in the particulate fraction increased approximately three-fold within 5 min, and declined to nearly zero between 20 and 60 min. Cytosolic activity increased in a biphasic manner, with an initial increase at 5 min, a decline at 10 min, and a further increase by 20 min, which was sustained for at least 60 min. By contrast, 12-O-tetradecanoylphorbol-13-acetate caused a rapid translocation of protein kinase C from cytosol to the particulate fraction which was sustained for at least 1 h. The results suggest that agents, such as phytohemagglutinin, which both generate diacylglycerol and mobilize intracellular Ca2+ stores, result in changes in subcellular distribution and activity of protein kinase C which are different from those elicited by 12-O-tetradecanoylphorbol-13-acetate.     

Comparative study of methods for the quantification of fungal spores at the leaf surfaces ofPopulus xeuramericana

Summary The removal of fungal spores, urediniospores ofMelampsora medusae and conidia ofPestalozzia sp., from the leaf surfaces ofPopulus xeuramericana (Dode) Guinier cv. I-488 was assessed using three cultural techniques conventionally employed in phylloplane studies. The method of removal and the original density of spore deposition, but not the interaction of these factors, were significant determinants of variability in spore removal. Irrespective of the original density of deposition, the leaf print method was the most, and the leaf washing technique the least, efficient means of spore removal from the leaf surface. Factors which could contribute to this difference in efficiency are discussed.     

中国鲤科鱼类染色体组型的研究 Ⅱ.鲴亚科四种鱼的染色体组型

鲴亚科(Xenocyprininae)鱼类多为中小型鱼类,常见于江河湖泊等较宽阔的水域中,我国长江、黑龙江、黄河及珠江诸流域皆有分布,共有10种,隶属4个属(伍献文等,1964)。迄今尚未见有该亚科鱼类染色体组型的研究报道。本文是对其中三属四种鱼的染色体组型的观察结果。这四种鱼是银鲴(Xenocypris argentea)、黄尾鲴(Xenocypris davidi)、细鳞斜颌鲴(Plagiognathops microlepis)和逆鱼(Acanthobrama simoni)。其中黄尾鲴和细鳞斜颌鲴均为新的淡水养殖鱼(沈德长等,1981;陈楚星,1979)。     

植物冷锻炼对于胁强敏感度的影响(英文)

前文由柑桔枝条在不同低温下、不同冷冻时间的电解质外渗测定,提出胁强(stress)、作用时间与胁变(strain)之间关系的数学模型。在这个模型中共有3个参数:屈服点温度(yield point temperature),胁强敏感度(stress sensitivity)和作用时间敏感度(sensitivity to duration),用以描述植物的抗性。抗性强的植物应表现为屈服点温度较低,胁强敏感度或者时间敏感度较低。为验证此数学模型,本工作以经冷锻炼与未经冷锻炼的盆栽柑桔枝条为材料,作不同温度与时间处理的电解质外渗率的测定,研究了冷锻炼对于上述3个参数的影响。发现胁强敏感度和屈服点温度受冷锻炼影响而下降,时间敏感度未表现明显变化。对于田间柑桔、油桐与毛竹的定期测定,在固定冷冻时间下,得到了类似于盆栽柑桔的结果。入冬时,植物抗冻性提高,3种植物都表现出下列两种变化:1.胁强敏感度的明显下降;2.屈服点温度和/或时间敏感度亦下降。开春时的变化则相反。胁强敏感度的变化与后一种变化有各自的规律,且因植物种类而不同。拐点胁强(stress at inflection point)具有与半致死温度(50％killing point temperature)不同的意义,它的变化是上述两种变化的综合结果。本试验结果表明,冷锻炼对于植物胁强敏感度有明显影响,用本数学模型的3个抗性指标描述     

微生物发酵法生产S-腺苷甲硫氨酸的研究进展

S-腺苷甲硫氨酸(S-adenosyl-l-methionine, SAM)广泛存在于生物体内,主要参与生物体内的转甲基过程、转硫过程及转氨丙基过程,具有重要的生理功能,其生产备受重视。目前SAM生产的研究主要集中于微生物发酵法,该方法与化学合成法和酶催化法相比,成本较低且更容易实现工业化生产。随着需求量的迅速增加,通过菌种改良提高SAM产量备受关注。当前SAM生产菌种改良的主要策略包括常规育种和代谢工程。本文综述了提高微生物生产SAM能力的近期研究进展并探讨了SAM生产中的瓶颈问题及解决方法,以期为进一步提高SAM产量提供思路。     

Biochemical and genetic characterization of three hamster cell mutants resistant to diphtheria toxin

We describe here three different hamster cell mutants which are resistant to diphtheria toxin and which provide models for investigating some of the functions required by the toxin inactivates elongation factor 2 (EF-2). Cell-free extracts from mutants Dtx(r)-3 was codominant. The evidence suggests that the codominant phenotype is the result of a mutation in a gene coding for EF-2. The recessive phenotype might arise by alteration of an enzyme which modifies the structure of EF-2 so that it becomes a substrate for reaction with the toxin. Another mutant, Dtx(r)-2, contained EF-2 that was sensitive to the toxin and this phenotype was recessive. Pseudomonas aeruginosa exotoxin is known to inactivate EF-2 as does diphtheria toxin and we tested the mutants for cross-resistance to pseudomonas exotoxin. Dtx(r)-1 and Dtx(r)-3 were cross-resistant while Dtx(r)-2 was not. It is known that diphtheria toxin does not penetrate to the cytoplasm of mouse cells and that these cell have a naturally occurring phenotype of diphtheria toxin resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance of the hybrid cells to diphtheria toxin. Intraspecies hybrids containing the genome of mutants Dtx(r)-1 and Dtx(r)-3 had some resistance while those formed with Dtx(r)-2 were as sensitive as hybrids derived from fusions between wild-type hamster cells and mouse 3T3 cells.     

Alternative metabolic fates of thymine nucleotides in human cells.

Three types of experiments have been used to study the metabolism of thymine nucleotides by human cells. (1) Cells were labelled continuously with [3H]thymidine and the incorporation of label into DNA compared with the specific radioactivities of pools of individual thymine nucleotides separated by chromatography on polyethylene-imine-cellulose. (2) Cellular thymine nucleotides were labelled with [3H]thymidine at 13 degrees C, followed by incubation at 37 degrees C in unlabelled medium. Incorporation of label into DNA and loss of label from the nucleotide pools were monitored during the 'chase' period at 37 degrees C. (3) The experiments described in (2) above were repeated in the presence of the DNA-synthesis inhibitor cytosine arabinoside, in order to demonstrate more clearly and to quantify degradative pathways for thymine nucleotides. In phytohaemagglutinin-stimulated lymphocytes and in bone-marrow cells, only a proportion (25-60%) of labelled thymine nucleotide was incorporated into DNA, the rest being rapidly degraded and lost from the cell. In contrast, an established cell line (HPB-ALL) from a patient with acute lymphoblastic leukaemia of thymic origin incorporated 100% of its exogenously labelled thymine nucleotides into DNA. These results indicated that alternative metabolic routes are open to thymine nucleotides in human cells. In lymphocytes from patients with megaloblastic anaemia and in normal lymphocytes treated with methotrexate, the utilization of labelled thymine nucleotides for DNA synthesis was more efficient than in controls. These results offer an explanation for the observation of a normal pool of thymidine triphosphate in the cells of patients with untreated megaloblastic anaemia even though the amount of this compound available for DNA synthesis appears to be decreased.     

Urea hydrolysis in some tea soils

The influence of application of hexachlorocyclohexane (HCH=gamma BHC), to a submerged tropical field soil at rates equivalent to recommended field rates (1–2.5kg a.i./ha) and twice this level, upon the rhizosphere soil nitrogenase, nitrogen fixers, and soil redox potential (Eh) was investigated. The rhizosphere soil from HCH-treated field exhibited significantly higher nitrogenase activity than that from untreated fields. HCH retarded the drop in redox potential of the field soil upto 80 days after transplantation under submerged conditions. Populations of nitrogen-fixingAzospirillum sp. and Azotobacter, to a greater extent, and anaerobic organisms, to a lesser extent, were stimulated in HCH-treated soils. Results indicate the stimulation of heterotrophic nitrogen-fixing bacteria by HCH in submerged paddy soils.