ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2307327

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

ADP is known to induce platelet shape change, aggregation, and exposure of fibrinogen binding sites as well as inhibit stimulated adenylate cyclase. The platelet is unique in that its purinergic receptor prefers ADP over ATP, which functions as a competitive antagonist. The affinity reagent, 5'‐p‐fluorosulfonylbenzoyl adenosine (FSBA), has been used to covalently label a single membrane protein, aggregin, on the external platelet surface with mol wt of 100 kDa. Concomitant with incorporation of FSBA, ADP‐induced shape change, aggregation, and fibrinogen binding is inhibited. FSBA is also a weak agonist at short times and high concentration, which suggests that prior noncovalent binding to aggregin takes place before covalent modification. Aggregin differs from platelet glycoprotein IIIa in its physical and immunochemical properties. Aggregin is distinct from the receptor coupled to adenylate cyclase. Using FSBA as a probe, platelet aggregation by thromboxane A2analogs and collagen was shown to be dependent on ADP but not the shape change induced by these agonists. Binding to aggregin is required for epinephrine‐induced aggregation. In turn, epinephrine increases the affinity of ADP for its receptor. Thrombin at concentrations greater than 2 nM (0.2 units/ml) stimulates platelet aggregation independent of ADP, but by raising cytoplasmic Ca2+it activates platelet calpain, which in turn cleaves aggregin. Thus aggregin, in addition to serving as the ADP receptor linked to shape change and aggregation, plays a role in fibrinogen receptor latency that is relieved entirely by ADP binding to or proteolysis of aggregin.— Colman, R. W. Aggregin: a platelet ADP receptor mediating activation.FASEB J.4: 1425‐1435; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2407587

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Homeobox‐containing genes, the homeogenes, are transcriptional regulators conserved in numerous animal groups. In the fruit fly they specify the identity of certain spatial units of development. We present a somewhat subjective summary of the advance triggered in vertebrate developmental biology by the discovery of the homeobox. Emphasis is placed on one group, theAntp (Antennapedia)‐like homeogenes.Antp‐like homeogenes are expressed in overlapping longitudinal areas of the neuroectoderm and mesoderm. The genomic organization of these genes is most uniquely connected with their expression. They are organized into unlinked clusters of 8‐10 loci. The linear order of genes within the clusters is highly conserved both among clusters within a species and among clusters of distant species. Expression of these genes along the longitudinal body axis uniformly follows a 5‘‐posterior‐3‘‐anterior rule. Their anterior border of expression stops abruptly at the hindbrain. A hypothesis is proposed, which suggests that much of the mid‐ and hindbrain, as well as the craniofacial structures, are newly acquired in the evolution of vertebrates, and do not utilize the more ancientAntp‐like homeogenes. We assume that these organs have a different group or groups of spatially specific transcriptional regulators.—Lonai, P., Orr‐Urtreger, A. O. Homeogenes in mammalian development and the evolution of the cranium and central nervous system.FASEB J.4: 1436‐1443; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.1968407

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Antibodies are produced exclusively in B lymphocytes. The expression of the antibody‐encoding genes, the immunoglobulin (Ig) genes, is also restricted to B cells. The octamer sequence ATGCAAAT is present in the promoter and the enhancer of Ig genes, and plays an important role in its tissue‐specific expression. This sequence motif is a binding site for nuclear proteins, the so‐called octamer transcription factors (Oct or OTF factors). The Oct‐1 protein is present in all cell types analyzed so far, whereas Oct‐2A and Oct‐2B are found mainly in B lymphocytes. All three proteins show the same sequence specificity and binding affinity. It appears that the B cell‐specific expression of Ig genes is mediated at least in part by cell type‐specific Oct factors, and that there are both quantitative and qualitative differences between Oct‐1 and Oct‐2 factors. Recently, a number of other octamer factor variants were identified. Many of these may be created by alternative splicing of a primary transcript of one Oct factor gene and may serve a specific function in the fine tuning of gene expression.— Kemler, I.; Schaffner, W. Octamer transcription factors and the cell‐type specificity of immunoglobulin gene expression.FASEB J.4: 1444‐1449; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2407588

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Cobalamin‐dependent methionine synthase catalyzes the transfer of a methyl group from N5‐methyltetrahydrofolate to homocysteine, producing tetrahydrofolate and methionine. Insufficient availability of cobalamin, or inhibition of methionine synthase by exposure to nitrous oxide, leads to diminished activity of this enzyme. In humans, severe inhibition of methionine synthase results in the development of megaloblastic anemia, and eventually in subacute combined degeneration of the spinal cord. It also results in diminished intracellular folate levels and a redistribution of folate derivatives. In this review, we summarize recent progress in understanding the catalysis and regulation of this important enzyme from both bacterial and mammalian sources. Because inhibition of mammalian methionine synthase can restrict the incorporation of methyltetrahydrofolate from the blood into cellular folate pools that can be used for nucleotide biosynthesis, it is a potential chemotherapeutic target. The review emphasizes the mechanistic information that will be needed in order to design rational inhibitors of the enzyme.—Banerjee, R. V.; Matthews, R. G. Cobalamin‐dependent methionine synthase.FASEB J.4: 1450‐1459; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2407589

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

A combination of cell‐free biochemical and morphological studies has revealed that a coated bud‐coated vesicle transport system shuttles newly synthesized proteins through the successive processing compartments of the Golgi apparatus. These Golgi‐coated vesicles operate in a manner formally analogous to the clathrin‐coated, pit‐coated vesicle system responsible for receptor‐mediated endocytosis; however Golgi‐coated vesicles do not contain clathrin.—Rothman, J. E.; Orci, L. Movement of proteins through the Golgi stack: a molecular dissection of vesicular transport.FASEB J.4: 1460‐1468; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2407590

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The major type of receptor for the inhibitory neurotransmitter γ‐aminobutyric acid (GABA), called the GABAAreceptor, is a member of a gene superfamily of ligand‐gated ion channels. This receptor is a heterooligomeric protein composed of several distinct polypeptide types (α, β, γ, andδ). Molecular cloning of these polypeptides reveals that they show 20‐40% identity with each other, and 10‐20% identity with polypeptides of the nicotinic acetylcholine receptors and strychnine‐sensitive glycine receptor. Each polypeptide type is also represented by a family of genes whose members have 60‐80% amino acid sequence identity. Regions of conserved and variable amino acid sequence suggest structural and functional domains within each polypeptide. All of the polypeptides when expressed in heterologous cells produce GABA‐activated chloride channels, and the different subtypes express different pharmacological properties. The distributions of mRNAs for the different GABAAreceptor polypeptides and their subtypes show significant brain regional variation consistent with pharmacological and biochemical evidence for receptor heterogeneity. Subpopulations of GABAAreceptors with different cellular and regional locations show differential sensitivity to GABA, to modulators like steroids, to physiological regulation, to disease processes, and to pharmacological manipulation by drugs such as benzodiazepines. The properties of the different subpopulations of GABAAreceptors are determined by which one or more of the different polypeptides and their subtypes are expressed in a given cell to produce a variety of different oligomeric protein structures. Molecular cloning techniques have produced rapid advances in understanding the GABAAreceptor protein family.— Olsen, R. W.; Tobin, A. J. Molecular biology of GABAAreceptors.FASEB J.4: 1469‐1480; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2155149

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

This study gives an account of the biologic and kinetic binding properties of interleukin 1α (IL 1α), interleukin 1β (IL 1β), and Glu‐4 (an NH2‐terminal mutant of IL 1β) to interleukin 1 (IL 1) receptors in rabbit articular chondrocytes. All three IL 1's demonstrated full agonist properties in their ability to stimulate prostaglandin E2(PGE2) synthesis. IL 1α was 23‐fold more biologically active than IL 1β, which was around 110‐fold more active than Glu‐4 based on the concentration of IL 1 required for half‐maximal stimulation of PGE2. The binding of all three ligands was concentration‐dependent and saturable at 4°C. Scatchard analysis of receptor binding data showed that the dissociation constant (KD) of IL 1α was 46 ± 12 pM, and the receptor density was 3120 sites/cell. The association of IL 1α at 4°C did not attain equilibrium until after 10 h at 100 pM of125I‐labeled IL 1α. The dissociation of bound IL 1α was very slow,t1/2of 21 h, although only one class of high‐affinity receptors was detected. TheKDof IL 1β binding was 72 ± 3 pM with a receptor density of 800 ± 40 sites/cell. Dissociation of bound125I‐labeled IL 1β at 4°C appeared to indicate the presence of two receptor subsets, a fast and a slower component with at1/2of 2 min and 5 h, respectively. The receptor binding affinity of Glu‐4 was 324 ± 3 pM, in line with its reduced biologic activity. Both IL la and IL 1β are rapidly internalized in chondrocytes in a time‐ and temperature‐dependent manner.— Chin, J. E.; Horuk, R. Interleukin 1 receptors on rabbit articular chondrocytes: relationship between biological activity and receptor binding kinetics.FASEB J.4: 1481‐1487; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2137805

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The formation of new membrane vesicles normally occurs during eukaryotic organellogenesis and maturation of bacteriophage PM2. This virus was studied as a simple model for membrane morphogenesis. Previous biochemical and genetic studies suggest that a major structural protein of PM2, sp6.6, is an integral membrane protein involved in viral membrane morphogenesis. To establish the necessity of sp6.6 in membrane formation, restriction fragments of PM2 that contained the sp6.6 coding sequence were cloned into several plasmid vectors for expression inEscherichia coli. Aconstruction in pBR322 containing twoHindIII fragments of PM2 DNA caused production of intracellular membrane vesicles of the same size as those produced in the course of natural infection ofAlteromonas espejiana.Similar results were obtained with a smaller construct ofHindII fragments in the plasmid vector pPL‐λ. Expression of sp6.6 was detected via incorporation of35S‐labeled methionine after SDS‐polyacrylamide gel electrophoresis and with a specific rabbit antiserum on immunoblots. Other constructs did not produce recognizable vesicles or sp6.6. These results are the first to suggest that a hydrophobic membrane protein can cause development of new membrane structure.— Armour, G. A.; Brewer, G. J. Membrane morphogenesis from cloned fragments of bacteriophage PM2 DNA that contain the sp6.6 gene.FASEB J.4: 1488‐1493; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2407591

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Accumulation of cyclic GMP in cultured rat lung fibroblasts was used to test the hypothesis that N1E‐115 neuroblastoma cells produce an endothelium‐derived relaxing factor (EDRF)‐like activity. By using this assay, the production of an EDRF‐like activity in homogenates and cytosolic fractions of N1E‐115 neuroblastoma cells was observed. Detection of the activity required the presence of superoxide dismutase and was inhibited by hemoglobin. Production of the EDRF‐like factor was dependent on L‐arginine and NADPH. The apparentKmfor L‐arginine was 1.25 μM and the apparentKmfor NADPH was 1.67 μM. The production of the EDRF‐like activity was inhibited by the L‐arginine analogs, NG‐monomethyl‐L‐arginine and NG‐nitro‐L‐arginine, with apparentKivalues of 1.0 and 0.3 μM, respectively.— Gorsky, L. D.; Forstermann, U.; Ishii, K.; Murad, F. Production of an EDRF‐like activity in the cytosol of N1E‐115 neuroblastoma cells.FASEB J.4: 1494‐1500; 1990.

ISSN:0892-6638    

DOI:10.1096/fasebj.4.5.2155150

出版商:Wiley    

年代:1990

数据来源: WILEY