A glycan-phosphatidylinositol-specific phospholipase D in human serum

A group of proteins anchored to the cell by phosphatidylinositol (PI) has recently been identified. The significance of this new class of membrane anchor is unknown; one possibility is that it facilitates release of the molecule by phospholipases. In fact, phospholipase C enzymes specific for the complex carboxyl-terminal glycolipids of these proteins have been isolated from African trypanosomes and from hepatocyte plasma membranes. This study reports the discovery of a glycan-PI-specific phospholipase D in human serum that cleaves both the membrane form of the variant surface glycoprotein of African trypanosomes and its glycolipid precursor, but not phosphatidylethanolamine, phosphatidylcholine, or phosphatidylinositol. Decay-accelerating factor, another PI-anchored molecule, is also cleaved by the enzyme and converted from a hydrophobic to a soluble protein. The enzyme is Ca2+-dependent, heat labile, and not affected by the inhibitor of serine proteases, phenylmethylsulfonylfluoride. Its function is not known, but the present findings indicate that it participates in the metabolism of glycolipid-anchored membrane proteins.     

意大利蜜蜂蜂毒磷脂酶A2基因在大肠杆菌中的表达

将意大利蜜蜂蜂毒磷脂酶A2(AmPLA2)成熟肽编码区基因(405 bp) 插入表达载体pETBlue-1,在大肠杆菌Tuner(DE3)placⅠ中诱导表达,经SDS-PAGE电泳检测,表达产物分子量为15 kD,约占细菌总蛋白的4.3%;用兔抗AmPLA2多克隆血清为第一抗体作Western blot检测,表达产物显示与天然AmPLA2同样的特异性印迹,证实AmPLA2 基因已在大肠杆菌中得到表达.     

Induction of interleukin 2 messenger RNA inhibited by cyclosporin A

Cyclosporin A blocked production of the lymphokine interleukin 2 by activated T lymphocytes. In a human and a murine cell line this inhibition reflected an absence of interleukin 2 messenger RNA. Under conditions in which these cells are normally stimulated to secrete high levels of interleukin 2, they failed to do so in the presence of cyclosporin A. In both cell lines this failure was accompanied by an absence of interleukin 2 messenger accumulation.     

Ultrastructure of secretory and high-polymer serum immunoglobulin A of human and rabbit origin

Electron micrographs of immunoglobulins A from human and rabbit colostrum, which were purified on tall agarose columns, revealed Y-shaped molecules (125 by 140 angstroms). The linear dimensions of the arms were 55 to 75 by 25 to 30 angstroms. A molecular model is postulated in which two immunoglobulin A monomers are superimposed on each other in a close-packed state with the secretory piece inserted in the constant region of the alpha-chains. High-polymer (11 or 13S) immunoglobulin A molecules (total span 100 to 110 angstroms) from human serum were composed of four arms (50 to 55 by 20 angstroms) joined at a contrast-rich center.     

Gamma interferon synthesis by human thymocytes and T lymphocytes inhibited by cyclosporin A

Cyclosporin A depresses the synthesis of gamma interferon by human thymocytes and T lymphocytes in vitro. This observation is of potential clinical significance because the long-term treatment of transplant patients with cyclosporin A, a widely used immunosuppressive agent, can give rise to B-cell lymphoma resulting from Epstein-Barr virus activation.     

A G protein mutant that inhibits thrombin and purinergic receptor activation of phospholipase A2

The stimulation of phospholipase A2 by thrombin and type 2 (P2)-purinergic receptor agonists in Chinese hamster ovary cells is mediated by the G protein Gi. To delineate alpha chain regulatory regions responsible for control of phospholipase A2, chimeric cDNAs were constructed in which different lengths of the alpha subunit of Gs (alpha s) were replaced with the corresponding sequence of the Gi alpha subunit (alpha i2). When a carboxyl-terminal chimera alpha s-i(38), which has the last 38 amino acids of alpha s substituted with the last 36 residues of alpha i2, was expressed in Chinese hamster ovary cells, the receptor-stimulated phospholipase A2 activity was inhibited, although the chimera could still activate adenylyl cyclase. Thus, alpha s-i(38) is an active alpha s, but also a dominant negative alpha i molecule, indicating that the last 36 amino acids of alpha i2 are a critical domain for G protein regulation of phospholipase A2 activity.     

苏木水提物抗蛇毒磷脂酶A2活性研究

中药苏木(Sappan Lignum)来源于植物苏木(Caesalpinia sappan L.)的干燥心材,具有止血 抗炎等功效。采用琼脂糖平板法研究不同浓度的苏木水提物（0.03g/ml,0.06g/ml,0.09g/ml, 0.12g/ml,0.15g/ml）对蛇毒sPLA2水解活性的抑制作用,测量透明圈和孔的直径,根据酶活标准曲 线计算其抑制率。结果表明0.15g/ml 苏木水提物对五步蛇毒sPLA2水解活性有抑制作用。     

Platelet-activating factor-induced aggregation of human platelets specifically inhibited by triazolobenzodiazepines

Platelet-activating factor (PAF), a naturally occurring phospholipid, is a potent activator of various biological processes, including platelet aggregation. The mechanisms by which PAF acts are largely unknown, partly because of the lack of specific inhibitors for PAF-elicited responses. It was found that in washed human platelets the psychotropic triazolobenzodiazepine drugs alprazolam and triazolam potently inhibited PAF-induced changes in shape, aggregation, and secretion. The effects were specific for PAF activation, since the responses of human platelets to adenosine diphosphate, thrombin, epinephrine, collagen, arachidonate, and the calcium ionophore A23187 were not inhibited by the triazolobenzodiazepines. These psychotropic drugs should be useful in investigating the possibility that PAF or PAF-like phospholipids play a role in neuronal function and in elucidating biochemical mechanisms activated specifically by PAF in a variety of cells.     

Interaction of brain synaptic vesicles induced by endogenous Ca2+ -dependent phospholipase A2

Endogenous phospholipase A2 activity of brain synaptic vesicles was Ca2+ -dependent and was increased by prostaglandin F2 alpha, calmodulin, adenosine 3', 5' -monophosphate, and adenosine triphosphate, whereas the activity was inhibited by prostaglandin E2 in the absence or presence of calmodulin. Light-scattering measurements demonstrated that stimulation of the enzyme's activity correlated with the induction of vesicle-vesicle aggregation. The effects of these compounds on endogenous synaptic vesicle phospholipase A2 activity may imply a common end point of their purported neuromodulatory actions, and indicate that synaptic vesicle phospholipase A2 may play a central role in presynaptic neurotransmission.     

Enhanced activity and altered specificity of phospholipase A2 by deletion of a surface loop

Protein engineering and x-ray crystallography have been used to study the role of a surface loop that is present in pancreatic phospholipases but is absent in snake venom phospholipases. Removal of residues 62 to 66 from porcine pancreatic phospholipase A2 does not change the binding constant for micelles significantly, but it improves catalytic activity up to 16 times on micellar (zwitterionic) lecithin substrates. In contrast, the decrease in activity on negatively charged substrates is greater than fourfold. A crystallographic study of the mutant enzyme shows that the region of the deletion has a well-defined structure that differs from the structure of the wild-type enzyme. No structural changes in the active site of the enzyme were detected.     

Crystal structure of cobra-venom phospholipase A2 in a complex with a transition-state analogue

The crystal structure of a complex between a phosphonate transition-state analogue and the phospholipase A2 (PLA2) from Naja naja atra venom has been solved and refined to a resolution of 2.0 angstroms. The identical stereochemistry of the two complexes that comprise the crystal's asymmetric unit indicates both the manner in which the transition state is stabilized and how the hydrophobic fatty acyl chains of the substrate are accommodated by the enzyme during interfacial catalysis. The critical features that suggest the chemistry of binding and catalysis are the same as those seen in the crystal structure of a similar complex formed with the evolutionarily distant bee-venom PLA2.     

Crystal structure of bee-venom phospholipase A2 in a complex with a transition-state analogue

The 2.0 angstroms crystal structure of a complex containing bee-venom phospholipase A2 (PLA2) and a phosphonate transition-state analogue was solved by multiple isomorphous replacement. The electron-density map is sufficiently detailed to visualize the proximal sugars of the enzyme's N-linked carbohydrate and a single molecule of the transition-state analogue bound ot its active center. Although bee-venom PLA2 does not belong to the large homologous Class I/II family that encompasses most other well-studied PLA2s, there is segmental sequence similarity and conservation of many functional substructures. Comparison of the bee-venom enzyme with other phospholipase structures provides compelling evidence for a common catalytic mechanism.     

Immunoglobulin M and secretory immunoglobulin A: presence of a common polypeptide chain different from light chains

Unique polypeptide chains have been isolated from S-sulfonated light-chain fractions of human serum immunoglobulin M and colostral immunoglobulin A. Their electrophoretic mobilities, molecular weights, peptide maps, amino acid compositions, and antigenic determinants are very similar or perhaps identical but differ from those of light chains and secretory piece.     

步长脑心通胶囊对急性脑梗死患者血浆脂蛋白磷酯酶A2水平的影响

目的 观察步长脑心通胶囊对急性脑梗死患者不同时期血浆脂蛋白磷脂酶A2(Lp-PLA2)水平的影响.方法116例急性脑梗死患者随机分为对照组(56例)和观察组(60例),对照组采用常规疗法,观察组加用步长脑心通胶囊.监测两组患者治疗后1、2、4、8、12周的血浆Lp-PLA2水平.结果 治疗后两组上述观察时期血浆Lp-PLA2水平均低于治疗前,且观察组显著低于对照组,差异均有统计学意义(P＜0.01).结论 步长脑心通胶囊治疗急性脑梗死可降低血浆Lp-PLA2水平.     

用结构熵E和关联维数D2探讨若干蛋白质结构

分子结构的结构熵被定义为Ｅ＝ｌｎＮ（Ｎ－１）（Ｎ－２）２Ｖ，其中Ｎ是总原子数，Ｖ＝∏ｍｉｍａｘ（ｌｉ），ｍａｘ（ｌｉ）表示分子所在空间中ｉ方向分量的２原子间最大距离．分子结构的关联维数由Ｄｑ＝ｌｉｍε→０ｌｏｇＣｑ（ε）ｌｏｇε，其中Ｃｑ（ε）表示ｑ阶关联积分．从蛋白质数据库选出３０个蛋白质，根据上述定义计算它们的Ｅ和Ｄ２值，结果发现，结构熵随着原子数的增加而减少．因此，对于描述分子结构的复杂程度来说，Ｅ是一个新的、不同于热力学熵的量．我们研究了羧肽酶Ａ（Ｃａｒｂｏｘｙ－ｐｅｐｔｉｄａｓｅＡ）的Ｄｑ－ｑ谱，发现各自对应于长程和短程间的相互作用的２个不连续的相变点ｑｃ＝－１和ｑｃ＝２．５     

Generation of light from free electrons

Experiments with the interaction of a rectangular cross- section beam of electrons which is brought into contact with a metallic diffraction grat e ng produce light variable in wavelength throughout the visible spectrum. Con tinuous variation of the beam thickness shows that light is produced by electrons hundreds of wavelengths from the grating, if the side of the beam near the grating is in contact with it. The results can be accounted for by periodic accelerations of the electrons passing over the surface of the grating. These accelerations are caused by electrostatic forces which in turn are due to the average spacecharge of sheets of elec trons reflected from the grating surface, so that in their space- charge structure the periodicity of the grating rulings is preserved.     

Resolution of a signal transfer region from a general binding domain in gbeta for stimulation of phospholipase C-beta2

Signaling by guanine nucleotide-binding proteins (G proteins) involves sequential protein-protein interactions. G protein-betagamma subunit (Gbetagamma) interactions with phospholipase C-beta2 (PLC-beta2) were studied to determine if all Gbeta contacts are required for signaling. A peptide encoding Gbeta amino acid residues 86 to 105 stimulated PLC-beta2. Six residues (96 to 101) within this sequence could transfer signals and thus constitute a core signal transfer region. Another peptide, encoding Gbeta amino acid residues 115 to 135, did not substantially stimulate PLC-beta2 by itself but inhibited Gbetagamma stimulation, indicating that residues 115 to 135 constitute a general binding domain. Resolution of signal transfer regions from general binding domains indicates that all protein-protein contacts are not required for signal transfer and that it may be feasible to synthesize agonists and antagonists that regulate intracellular signal flow.     

油松和虎榛子不同林型根系分泌物组分及化感效应

采用气质联用（GC/MS）技术,分别对油松Piuns tabulaeformis纯林和虎榛子Ostryopsis davidiana纯林及两者混交林根际土壤中根系分泌物组分进行分析。在此基础上,应用外源法选择邻苯二甲酸、ρ-香豆酸对油松盆栽幼苗进行了化感效应测试。结果表明：根际中检测到的化合物包括有机酸类、酯类和酚酸类。其中有机酸是数量最多且比例最大的一类化合物,在油松纯林、虎榛子纯林及混交林中有机酸所占比例分别为63.82%,71.05%和69.12%;酯类分别占8.38%,12.65%和14.42%;酚酸类分别占整个组分的27.80%,16.30%和16.46%;酚酸类化合物检测到7种,包括羟基肉桂酸、ρ-羟基苯甲酸、4-羟基苯甲酸、邻苯二甲酸、3,4-二羟基苯甲酸、3,5-二羟基苯甲酸和ρ-香豆酸,混交林中没有检测到羟基肉桂酸。油松纯林中,7种酚酸的含量显著高于另外2种林型,除3,4-二羟基苯甲酸外,其余酚酸含量均为混交林的2.5倍以上,ρ-香豆酸达到8倍;与对照相比,应用外源ρ-香豆酸和邻苯二甲酸在质量浓度2.5 mg·L^－1时对油松苗高和生物量均具有促进作用,化感响应指数为正值。随着2种化合物质量浓度的增大,抑制作用加强,但ρ-香豆酸的抑制作用小于邻苯二甲酸。因此,混交林根际根系酚酸含量的降低可能是其生长优于纯林的重要原因之一。图2表1参12