稀土元素Pr~(3+)、Nd~(3+)对蚕豆(Vicia feba)叶片原生质膜上Ca~(2+)·Mg~(2+)-ATPase活性的影响

本文介绍用二相分配法制备蚕豆叶片原生质膜上的Ca~(2+)·Mg~(2+)-ATPase,用以研究镧系,稀土离子对此酶活性的影响。初步证实Pr~(3+)、Nd~(3+)对依赖于CaM的以及不依赖于CaM的蚕豆叶片原生质膜上Ca~(2+)·Mg~(2+)-ATPase活性的抑制不是CaM专一的。     

Dissociative inhibition of dimeric enzymes. Kinetic characterization of the inhibition of HIV-1 protease by its COOH-terminal tetrapeptide

Human immunodeficiency virus 1 (HIV-1) protease is an aspartyl protease composed of two identical protomers linked by a four-stranded antiparallel beta-sheet consisting of the NH2- and COOH-terminal segments (Weber, I.T. (1990) J. Biol. Chem. 265, 10492-10496). Kinetic analysis of the HIV-1 protease-catalyzed hydrolysis of a fluorogenic substrate demonstrates that the enzyme is an obligatory dimer. At pH = 5.0, 0.1 M sodium acetate, 1 M NaCl, 1 mM EDTA buffer, 37 degrees C, the equilibrium dissociation constant, Kd = 3.6 +/- 1.9 nM. We found that the tetrapeptide Ac-Thr-Leu-Asn-Phe-COOH, corresponding to the COOH-terminal segment of the enzyme, is an excellent inhibitor of the enzyme. Kinetic analysis shows that the inhibitor binds to the inactive protomers and prevents their association into the active dimer (dissociative inhibition). The dissociative nature of this inhibition is consistent with the results obtained from sedimentation equilibrium experiments in which the apparent molecular weight of the enzyme was observed to be 20,800 +/- 1,500 and 12,100 +/- 300, in the absence and presence of the COOH-terminal tetrapeptide, respectively. The dissociation constant of the protomer-inhibitor complex is Ki = 45.1 +/- 1.8 microM. This is the first kinetic analysis and direct experimental demonstration of noncovalent dissociative inhibition.     

IFN-alpha induces autocrine production of IL-6 in myeloma cell lines.

IL-6 is a major tumor growth factor in human multiple myeloma. Myeloma cell lines, which have the same phenotypic characteristics and Ig gene rearrangements as the original fresh myeloma cells and whose growth is strictly dependent on exogenous IL-6 similar to fresh myeloma cells, have been reproducibly established. We show here that IFN-alpha stimulated the growth of five of six of these human myeloma cell lines by inducing an autocrine production of IL-6 in myeloma cells. Indeed, IFN-alpha induced IL-6 mRNA accumulation and IL-6 production in myeloma cells and the IFN-alpha-induced growth of these cells was inhibited by anti-IL-6 mAb. Moreover, IFN-alpha made possible the rapid emergence of autonomously growing myeloma cell sublines, which produced IL-6 as an autocrine growth factor. As IFN-alpha has a potential therapeutical interest for multiple myeloma, the present study opens up new directions for studying its effects on the myeloma clone in vivo.     

Extracellular matrix (mesoglea) of Hydra vulgaris. II. Influence of collagen and proteoglycan components on head regeneration.

Hydra are characterized by having their body wall organized as an epithelial bilayer with an intervening acellular layer termed the mesoglea. As an extension of the previous study which indicated that mesoglea is a primitive basement membrane which has retained some characteristics of interstitial extracellular matrix, the present study was undertaken to analyze the role of mesoglea components during head regeneration in Hydra vulgaris. Studies were conducted that utilized drugs that affect collagen processing or secondary collagen structure (beta-aminoproprionitrile; 2,2'-dipydridyl; and cis-4-hydroxy-L-proline) and a drug that inhibits addition of glycosaminoglycan chains to proteoglycan core proteins (p-nitrophenyl-beta-D-xylopyranoside). These studies indicated that alterations in the structure of collagens or proteoglycans caused blockage of head regeneration in Hydra as monitored over a 48-hr period. Blockage of head regeneration was reversible once the drugs were removed, indicating that the drugs were not having a general toxic effect on the organism. Radiotracer studies also indicated that blockage of head regeneration was not simply due to a general depression of protein synthesis by the drugs. Various controls indicated that each drug was affecting mesoglea components under the conditions utilized in these studies. These observations indicate that preservation of normal mesoglea structure is required for Hydra head regeneration to proceed.     

Trigonal crystals of porin from Escherichia coli

Trigonal crystals of the integral membrane protein porin from Escherichia coli have been grown and characterized. They belong to space group P321 with unit cell constants a = b = LL8.4, c = 52.7 A, alpha = beta = 90 degrees, gamma = 120 degrees. The crystals grow as well-defined hexagonal prisms to a size of 0.25 mm in all dimensions, and diffract to 2.7 A. The molecular symmetry coincides with 3-fold crystallographic symmetry, giving two trimers per unit cell (1 monomer/asymmetric unit). This corresponds to VM = 2.9 A3/Da. Native X-ray data to 3.0 A resolution have been collected on a FAST area detector and a search for heavy atom derivatives is underway.     

与胎儿珠蛋白基因持续表达有关的(A_γδβ)°—地贫纯合子及杂合子的分子鉴别

我们分子鉴别了一个缺失型中国(A_γδβ)°-地贫家系。先证者为这一缺失的纯合子,具有中度贫血症状。家系的另五个成员均为这一缺失的杂合子,其胎儿血红蛋白(HbF)为16—21％,接近或达到HPFH杂合子的HbF水平,并且几乎不表现贫血症状。限制性内切酶图谱分析证明了β-珠蛋白基因簇内的DNA顺序缺失,缺失的5′端点位于Aγ基因IVSⅡ内,3′端点在β-珠蛋白基因下游区远端,距HPFH-2的3′缺失端点上游区约11kb。缺失的总长度约为80kb。本文讨论了这一缺失导致胎儿血红蛋白在成人中持续活跃表达的可能机制。     

基因定点诱变删除及天然α型心钠素的分泌型表达

用基因定点诱变技术,删除了pO_1α ANF表达质粒中的33对碱基,使人α型心钠素结构基因直接与大肠杆菌分泌型表达质粒pIN-Ⅲ-OmPA中的信号肽酶切位点编码区相连,构成天然人α型心钠素的表达质粒pANF,在IPTG诱导下表达28肽的天然人α型心钠素。纯化后的表达产物具有天然心钠素的放免活性和很强的舒张血管的生物活性。     

Molecules,fossils, and the origin of tetrapods

Summary Since the discovery of the coelacanth, Latimeria chalumnae, more than 50 years ago, paleontologists and comparative morphologists have debated whether coelacanths or lungfishes, two groups of lobe-finned fishes, are the closest living relatives of land vertebrates (Tetrapoda). Previously, Meyer and Wilson (1990) determined partial DNA sequences from two conservative mitochondrial genes and found support for a close relationship of lungfishes to tetrapods. We present additional DNA sequences from the 12S rRNA mitochondria gene for three species of the two lineages of lungfishes that were not represented in the first study: Protopterus annectens and Protopterus aethiopicus from Africa and Neoceratodus forsteri (kindly provided by B. Hedges and L. Maxson) from Australia. This extended data set tends to group the two lepidosirenid lungfish lineages (Lepidosiren and Protopterus) with Neoceratodus as their sister group. All lungfishes seem to be more closely related to tetrapods than the coelacanth is. This result appears to rule out the possibility that the coelacanth lineage gave rise to land vertebrates. The common ancestor of lungfishes and tetrapods might have possessed multiple morphological traits that are shared by lungfishes and tetrapods [Meyer and Wilson (1990) listed 14 such traits]. Those traits that seem to link Latimeria and tetrapods are arguably due to convergent evolution or reversals and not to common descent. In this way, the molecular tree facilitates an evolutionary interpretation of the morphological differences among the living forms. We recommended that the extinct groups of lobe-finned fishes be placed onto the molecular tree that has lungfishes and not the coelacanth more closely related to tetrapods. The placement of fossils would help to further interpret the sequence of morphological events and innovations associated with the origin of tetrapods but appears to be problematic because the quality of fossils is not always high enough, and differences among paleontologists in the interpretation of the fossils have stood in the way of a consensus opinion for the branching order among lobefinned fishes. Marshall and Schultze (1992) criticized the morphological analysis presented by Meyer and Wilson (1990) and suggest that 13 of the 14 morphological traits that support the sister group relationship of lungfishes and tetrapods are not shared derived characters. Here we present further alternative viewpoints to the ones of Marshall and Schultze (1992) from the paleontological literature. We argue that all available information (paleontological, neontological, and molecular data) and rigorous cladistic methodology should be used when relating fossils and extant taxa in a phylogenetic framework. Offprint requests to: Axel Meyer     

Characterisation and Regional Localisation of Pre- and Postsynaptic Glycoproteins of the Chick Forebrain Showing Changed Fucose Incorporation Following Passive Avoidance Training

To identify those glycoproteins whose synthesis or modification is necessary for memory formation, we have studied the uptake of radiolabelled fucose into synaptic plasma membranes (SPMs) and postsynaptic densities (PSDs) derived from two specific left and right forebrain loci, at two different times after training of 1-day-old chicks on a one-trial passive avoidance learning task. To increase the reliability of the comparison, a double-labelling method was used. Tissue samples from intermediate medial hyperstriatum ventrale (IMHV) and lobus parolfactorius (LPO) were isolated at 6 and 24 h after training. At both times, training resulted in region-specific changes, both increases and decreases, in incorporated radioactivity into pre- and postsynaptic glycoproteins. After 6 h, there was a relative decline in incorporation into both SPMs and PSDs of the right IMHV of trained chicks, a decline that persisted in the PSDs until 24 h. A small decline in incorporation in SPMs from the right LPO of trained chicks at 6 h was reversed by 24 h, by which time there was a 64% increase in incorporation into SPMs and a 24% increase into PSDs of the left LPO. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis of left and right hemisphere samples containing LPO revealed that 6 h after training the main effect was presynaptic, including a reduction of incorporation into high molecular mass glycoproteins, of 150-180 kDa, and an increase in a lower molecular mass (41 kDa) fraction. By 24 h after training, a left hemisphere presynaptic glycoprotein of molecular mass approximately 50 kDa showed the biggest increase in fucosylation. In addition, a wide group of postsynaptic glycoproteins of both hemispheres, in the ranges 150-180, 100-120, and 33 kDa now showed increases in incorporation. Some other fractions showed decreases. These results are in accord with previous data on incorporation obtained using the amnesic agent 2-deoxygalactose. They also support the hypothesis that memory formation involves the strengthening of connections between pre- and postsynaptic neurons of the LPO by growth or modulation of pre- and postsynaptic structures.