bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies related to the head‐maturation pathway of bacteriophages T4 and T2: I. Morphology and kinetics of intracellular particles produced by mutants in the maturation genes
Authors: Wunderli H. , v.d. Broek J. , Kellenberger E. 
Published: May 2005

AbstractMutants in the genes governing the maturation of the head of bacteriophage T4 and in gene 24 were studied by electron microscopy of thin sections. We define morphologically: black particles, comprising mature, stable heads and immature, fragile heads, which break down upon lysis; grizzled particles, which apparently are partially filled or partially emptied; empty large particles without DNA or core Which are all the same size as normal heads; empty small particles without DNA and without core which are of the size of the τ particle, which is the prehead of phage T4.The study of single and double mutants of the maturation genes demonstrates that the phenotypes are only different by the proportions of the different particles made except for 17− where only empty small and empty large particles accumulate. The mutants in gene 24 are epistatic on all other mutants. Mutants in gene 17 are epistatic on the remaining ones.The results are consistent with the hypothesis that the products of several of the maturation genes act on DNA to render it competent for packaging while the others act directly on the particle. By this uncoupling, bypasses and abortive pathways can result.
Effect of calcium on the pellet height response of Tetrahymena cilia
Authors: Blum J. J. , Hayes Alvernon 
Published: May 2005

AbstractThe pellet height response (a measure of the increase in height of the pellet of cilia obtained by brief centrifugation in the presence of ATP as compared to the absence of ATP) of Tetrahymena cilia prepared by deciliation in the presence of Ca2+ is sensitive to the concentration of free Ca2+ during the pellet height assay. The magnitude of the increase in pellet height and the sharpness of the pellet boundary both increase markedly with increasing [Ca2+]. The half‐maximal effect is attained at a free [Ca2+] of about 1.5 × 10−7 M. The pellet height assay thus measures a Ca2+‐sensitive component of the ciliary motile system. The possibility that this is the Ca2+‐sensitive orientation system is discussed.
Reconstitution of D‐glucose transport in vesicles composed of lipids and intrinsic protein (Zone 4.5) of the human erythrocyte membrane
Authors: Kahlenberg Arthur , Zala Cedric A. 
Published: May 2005

AbstractElucidation of the mechanism of facilitated D‐glucose transport in human erythrocytes is dependent on the identification and isolation of the membrane protein(s) mediating this process. Based on the fact that stereospecific D‐glucose transport is reconstituted in liposomes prepared by sonication of a lipid suspension with ghosts or fractions derived from ghosts, a quantitative assay for the stereospecific D‐glucose transport activity of these fractions was developed (Zala CA, Kahlenberg A: Biochem Biophys Res Commun 72:866, 1976). This assay was used to monitor the purification of ghosts. The solubilized membrane protein fraction was chromatographed on a column of diethylaminoethyl cellulose which was eluted stepwise with NaCl‐phosphate buffers of increasing ionic strength. A fraction, eluted at an ionic strength of 0.1, displayed a 13‐ and 27‐fold increase in reconstituted transport activity relative to ghosts and to the unfractionated Triton X‐100 extract, respectively. This fraction, when analyzed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, consisted predominantly of the ghost proteins with an apparent molecular weight of 55,000, commonly designated as zone 4.5; periodic acid‐Schiff‐sensitive membrane glycoproteins 1–4 were absent. Transport reconstituted by this preparation of zone 4.5 membrane proteins was almost completely abolished by 1‐fluoro‐2,4‐dinitrobenzene, mercuric chloride, and p‐chloromercuribenzene sulfonate, but was unaffected by sodium iodoacetate. Extra‐ and intraliposomal phloretin and cytochalasin B, respectively, exhibited partial inhibition. The stereospecificity and inhibition characteristics of the reconstituted transport imply that all the components of the erythrocyte D‐glucose transport system are contained in the zone 4.5 membrane protein preparation.
The molecular mechanism of dicarboxylic acid transport in escherichia coli K 12
Authors: Lo Theodore C. Y. 
Published: May 2005

AbstractIt is the purpose of this communication to review the properties of the dicarboxylic acid transport system in Escherichia coli K12, in particular the role of various dicarboxylate transport proteins, and the disposition of these components in the cytoplasmic membrane. The dicarboxylate transport system is an active process and is responsible for the uptake of succinate, fumarate, and malate. Membrane vesicles prepared from the EDTA, lysozyme, and osmotic shock treatment take up the dicarboxylic acids in the presence of an electron donor. Genetic analysis of various transport mutants indicates that there is only one dicarboxylic acid transport system present in Escherichia coli K12, and that at least 3 genes, designated cbt, dct A, and dct B, are involved in this transport system. The products corresponding to the 3 genes are: a periplasmic binding protein (PBP) specified by cbt, and 2 membrane integral proteins, SBP 1 and SBP 2, specified by dct B and dct A, respectively. Components SBP 1 and SBP 2 appear to be exposed on both the inner and outer surfaces of the membrane, and lie in close proximity to each other. The substrate recognition sites of SBP 2 and SBP 1 are exposed on the outer and inner surfaces of the membrane respectively. The data presently available suggest that dicarboxylic acids may be translocated across the membrane via a transport channel. A tentative working model on the mechanism of translocation of dicarboxylic acids across the cell envelope by the periplasmic binding protein, and the 2 membrane carrier proteins is presented.
Existence of a common precursor to ACTH and endorphin in the anterior and intermediate lobes of the rat pituaitary
Authors: Eipper Betty A. , Mains Richard E. 
Published: May 2005

AbstractExtracts of rat anterior and intermediate‐posterior pituitary were fractionated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and assayed for immunoactive ACTH and endorphin. In both lobes the major forms of immunoactive ACTH have apparent molecular weights of 31,000 (31K), 20–21K, 14K, and 4.5K, and the major forms of immunoactive endorphin have apparent molecular weights of 31K (coincident with the peak of immunoactive ACTH), 13K (a βLPH‐like peptide), and 3.5K (a β‐endorphin‐like peptide). However, the quantitative distribution of immunoactivity among the various forms differs greatly between the lobes. Assays using an extreme COOH‐terminal ACTH antiserum indicate that the 31K ACTH/endorphin molecule in rat antierior and intermediate pituitary is similar to the pro‐ACTH/endorphin molecule from mouse pituitary tumor cells. A radioimmunoassay that is specific for the NH2‐terminal non‐ACTH, nonendorphin segment (referred to as 16K fragment) of the mouse pro‐ACTH/endorphin molecule was used to assay extracts of rat pituitary. In addition to detecting material at 31K and 20–21K, the 16K fragment radioimmunoassay detects significant amounts of cross‐reactive material with an apparent molecular weight of 16K in extracts of both lobes. This result also suggests that the structure and processing of the rat 31K ACTH/endorphin molecule is similar to that of mouse tumor cell pro‐ACTH/endorphin.Cell suspensions were prepared from the anterior and intermediate lobes of the rat pituitary and maintained in culture for a 24‐h period. The isolated cells from both lobes incorporate [3H] phenylalanine into immunoprecipitable ACTH‐ and endorphin‐containing molecules. By sequential immunoprecipitation with ACTH and endorphin antisera, it is possible to demonstrate directly that a single molecule (31K ACTH/endorphin) has antigenic determinants for both ACTH and endorphin. Significant amounts of 31K ACTH/endorphin are released into the culture medium by isolated anterior lobe and intermediate lobe cells. The isolated intermediate lobe cells synthesize and secrete relatively large amounts of a β‐endorphin‐like molecule; the isolated anterior lobe cells secrete significant amounts of both a βLPH‐like molecule and a β‐endorphin like molecule. These same quantitative differences between anterior and intermediate lobe tissue were observed in immunoassays of extracts of the separated lobes and probably reflect differences in the processing of the common precursor. The isolated anterior lobe cells can be stimulated to release increased amounts of immunoprecipitable ACTH and endorphin by incubation with a cyclic AMP analog and a phosphodiesterase inhibitor.
Fine structure of the band 3 protein in human red cell membranes: Freeze‐fracture studies
Authors: Weinstein Ronald S. , Khodadad Jena K. , Steck Theodore L. 
Published: May 2005

AbstractThe major red cell membrane protein, band 3, is a glycoprotein which extends across the membrane from the extracellular space into the cytoplasmic compartment. It is widely held that band 3 is a component of the intramembrane particles (IMP) which can be demonstrated by freeze‐fracture electron microscopy. In this study, we find that the outer surface poles of the IMP can be seen by freeze‐etching after they are unmasked by proteolysis under conditions which excise the surrounding sialopeptides from the membrane. The poles appear as distinctive projections, 30–50 Å in diameter, the “ES particles.” The ES particles remain associated with the outer surface of the membrane following cleavage of the band 3 polypeptide by chymotrypsin or pronase. This is consistent with previous biochemical studies which have shown that the 38,000‐dalton outer surface segment of band 3 is intercalated in the lipid bilayer. A granulofibrillar component at the inner surface of the membrane is provisonally identified as the 40,000‐dalton inner‐surface domain of band 3.
Glucocorticoid‐mediated alteration in growth factor binding and action: Analysis of the binding change
Authors: Baker Joffre B. , Cunningham Dennis D. 
Published: May 2005

AbstractThe addition of the glucocorticoid analog dexamethasone (DX) to serum‐free cultures of human fibroblasts caused a twofold enhancement of the mitogenic response to epidermal growth factor (EGF), although DX by itself was not mitogenic. A basis for this effect was suggested by studies showing that DX also increased the cellular binding of 125I‐EGF. DX increased the ability of the cells to bind 125I‐EGF only at low physiological concentrations of this polypeptide. Thus, data from 125I‐EGF binding to cells incubated without DX produced a linear Scatchard plot, whereas the data from 125I‐EGF binding to DX‐treated cells led to an upwardly curvilinear Scatchard plot. Measurements of 125I‐EGF association with the cell surface and cytoplasm indicated that this binding change involved an alteration of cell surface EGF receptors. The binding change appeared not to involve negatively cooperative interactions between EGF receptors, nor a change in the number of receptors. The binding alteration could be explained by a model in which DX converted 25–30% of the cell surface EGF receptors to a form having a fourfold increased affinity.
Proteolytic cleavage and structural transformation: Their relationship in bacteriophage T4 capsid maturation
Authors: Steven Alasdair C. , Carrascosa Jose L. 
Published: May 2005

AbstractGiant T4 phage capsoids formed in canavanine‐treated cultures infected by phage mutants in genes 21 and 17, respectively, differ with regard to cleavage of the major capsid protein, gp 23, and in the fine structure of their hexagonal surface lattices. Quantitative computer processing of electron micrographs shows that the significant differences in capsomer morphology amount to six symmetrically placed features present in the uncleaved hexamer but absent after cleavage. These features may be related with the N‐terminal portions of gp 23 monomers excised by phage‐specific proteolysis. Cleaved 17− giants can be induced to undergo a further structural transformation (expansion). Structural characteristics of partially transformed giant particles give clues about the dynamics of the cleavage and expansion transformations. Both processes appear to be polar, initiating in one cap and propagating along the particle. The transition zone of partial cleavage is diffuse, whereas the transition between unexpanded and expanded areas is confined to a narrow band of some 20 nm width.
Growth factors and gangliosides: A possible new perspective in neuronal growth control
Authors: Morgan James I. , Seifert Wilfried 
Published: May 2005

AbstractFor many permanent cell lines the transition from a growing (P) to a resting (R) state is reversibly controlled by growth factors present in serum. This P‐to‐R transition was studied in a neuronal cell line (B 104) with respect to the action of serum, dibutyryl cyclic AMP (DBcAMP), gangliosides, and a glioma cell‐produced growth factor GGF. In this cell system gangliosides seem to act as differentiation and survival factors. The kinetics of uptake of radioactively labeled gangliosides and survival experiments both support the idea of the stable incorporation of exogenously added gangliosides into the cells. Based on the experimental evidence a new model of cell development is proposed. Thus in addition to the R or G0 state, which in this cell system is rather unstable and probably regulated by cyclic nucleotides, we postulate a differentiated D state, which is controlled by gangliosides and which is characterized by its stability (survival time). This D compartment seems to be closer to the in vivo differentiated neuron than does the R or P state. The possible mechanisms for the action of gangliosides are discussed.
Co‐translational modification of nascent immunoglobulin heavy and light chains
Authors: Bergman Lawrence W. , Kuehl W. Michael 
Published: May 2005

AbstractWe have investigated the in vivo co‐translational covalent modification of nascent immunoglobulin heavy and light chains. Nascent polypeptides were separated from completed polypeptides by ion‐exchange chromatography of solubilized ribosomes on QAE‐Sephadex. First, we have demonstrated that MPC 11 nascent heavy chains are quantitatively glycosylated very soon after the asparaginyl acceptor site passes through the membrane into the cisterna of the rough endoplasmic reticulum. Nonglycosylated completed heavy chains of various classes cannot be glycosylated after release from the ribosome, due either to rapid intramolecular folding and/or intermolecular assembly, which cause the acceptor site to become unavailable for the glycosylation enzyme. Second, we have shown that the formation of the correct intrachain disulfide loop within the first light chain domain occurs rapidly and quantitatively as soon as the appropriate cysteine residues of the nascent light chain pass through the membrane into the cisterna of the endoplasmic reticulum. The intrachain disulfide loop in the second or constant region domain of the light chain is not formed on nascent chains, because one of the cysteine residues involved in this disulfide bond does not pass through the endoplasmic reticulum membrane prior to chain completion and release from the ribosome. Third, we have demonstrated that some of the initial covalent assembly (formation of interchain disulfide bonds) occurs on nascent heavy chains prior to their release from the ribosome. The results are consistent with the pathway of covalent assembly of the cell line, in that completed light chains are assembled onto nascent heavy chains in MPC 11 cells (IgG2b), where a heavy‐light half molecule is the major initial covalent intermediate; and completed heavy chains are assembled onto nascent heavy chains in MOPC 21 cells (IgG1), where a heavy chain dimer is the major initial disulfide linked intermediate.
The detection, immunofluorescent localization, and thrombin induced release of human platelet‐associated fibronectin antigen
Authors: Ginsberg Mark H. , Painter Richard G. , Birdwell Charles , Plow Edward F. , Forsyth Jane 
Published: May 2005

AbstractPlatelets are cells which develop adhesive properties following stimulation. Since fibronectin (fn) mediates adhesive properties of several cells, we sought evidence for platelet associated fn. Lysates of suspensions of washed human platelets containing ≤50 ng soluble fn/109 cells contained 2.85 μg fn antigen per 109 cells. The platelet fn antigen competition curve showed a similar slope to the curve for purified plasma fn suggesting antigenic identity. Immunofluorescent staining for fn was minimal in intact cells suggesting that the majority of fn antigen is intracellular. In permeable platelets, fluorescent staining for fn was seen in a punctate distribution suggesting a granule localization. Stimulation of platelet secretion by thrombin released platelet fn antigen. Suramin, a drug which inhibits platelet secretion, inhibited fn release. The apparent secretion of platelet fn, taken with the immunofluorescent data, support the localization of a portion of platelet fn antigen in a storage granule.
Fibronectin and proteoglycans as determinants of cell‐substratum adhesion
Authors: Culp Lloyd A. , Murray Ben A. , Rollins Barrett J. 
Published: May 2005

AbstractWhen normal or SV40‐transformed Balb/c 3T3 cells are treated with the Ca++‐specific chelator EGTA, they round up and pull away from their footpad adhesion sites to the serum‐coated tissue culture substrate, as shown by scanning electron microscope studies. Elastic membranous retraction fibers break upon culture agitation, leaving adhesion sites as substrate‐attached material (SAM) (Cells leave “footprints” of substrate adhesion sites during movement by a very similar process.) SAM contains 1–2% of the cell's total protein and phospholipid content and 5–10% of its glucosamine‐radiolabeled polysaccharide, most of which is glycosaminoglycan (GAG). By one‐ and two‐dimensional sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, there is considerable enrichment in SAM for specific GAGs; for the glycoprotein fibronectin; and for the cytoskeletal proteins actin, myosin, and the subunit protein of the 10 nm‐diameter filaments. Fibrillar fibronectin of cellular origin and substratum bound fibronectin of serum origin (cold‐insoluble globulin, CIg) have been visualized by immunofluorescence microscopy. The GAG composition in SAM has been examined under different cellular growth and attachment conditions. Heparan sulfate content correlates with glycopeptide content (derived from glycoprotein). Newly attaching cells deposit SAM with principally heparan sulfate and fibronectin and little of the other GAGs. Hyaluronate and chrondroitin proteoglycans are coordinately deposited in SAM as cells begin spreading and movement over the substrate. Cells attaching to serum‐coated or CIg coated substrates deposited SAM with identical compositions. The proteoglycan nature of the GAGs in SAM has been examined as well as the ability of proteoglycans to form two classes of reversibly dissociable “supramolecular complexes” ‐ one class with heparan sulfate and glycopeptide‐containing material and the second with hyaluronate‐chondroitin complexes. Enzymatic digestion of “intact” SAM with trypsin or testicular hyaluronidase indicates that (1) only a small portion of long‐term radiolabeled fibronectin and cytoskeletal protein is bound to the substrate via hyaluronate or chondroitin classes of GAG; (2) most of the fibronectin, cytoskeletal protein and heparan sulfate coordinately resist solubilization; and (3) newly synthesized fibronectin, which is metabolically labile in SAM, is linked to SAM by hyaluronate‐ and/or chondroitin‐dependent binding. All of our studies indicate that heparan sulfate is a direct mediator of adhesion of cells to the substrate, possibly by binding to both cell‐surface fibronectin and substrate‐bound CIg in the serum coating; hyaluronate‐chondroitin complexes in SAM appear to be most important in motility of cells by binding and labilizing fibronectin at the periphery of footpad adhesions, with subsequent cytoskeletal disorganization.
Possible role of fibronectin in malignancy
Authors: Chen Lan Bo , Summerhayes Ian , Hsieh Philip , Gallimore Philip H. 
Published: May 2005

AbstractFrozen sections of tumors induced by injecting virally transformed cells into animals were stained for fibronectin by immunofluorescence. Many tumor cell lines do not express fibronectin in tumors in situ even though some of them express fibronection in culture. Cell shape and hormones appear to influence the expression of fibronectin in culture; however, it is nuclear how fibronection expression is regulated in vivo.
Regulation of the Balb/c‐3T3 cell cycle‐effects of growth factors
Authors: Stiles C. D. , Pledger W. J. , Tucker R. W. , Martin R. G. , Scher C. D. 
Published: May 2005

AbstractThe platelet‐derived growth factor (PDGF), which is found in serum but not in plasma, has been purified to homogeneity; it stimulates replication at a concentration of 10−10M. Brief treatment with PDGF causes densityinhibited Balb/c‐3T3 cells to become competent to synthesize DNA; pituitary fibroblast growth factor (FGF) or precipitates of calcium phosphate also induce competence. Continuous treatment with plasma allows competent, but not incompetent, cells to synthesize DNA. A critical component of plasma is somatomedin, a group of hormones with insulin‐like activity; multiplication‐stimulating activity (MSA) or insulin replace plasma somatomedin in promoting DNA synthesis.We have studied the molecular correlates of competence and the role of SV40 gene A products in regulating DNA synthesis. Treatment of quiescent cells with pure PDGF or FGF causes the preferential synthesis of five cytoplasmic proteins (approximate molecular weight 29,000, 35,000, 45,000, 60,000, and 72,000 detected by SDS‐PAGE under reducing conditions). Two of these competence‐associated proteins (29,000 and 35,000 daltons) are found within 40 min of PDGF addition; they are not induced by plasma, insulin, or epidermal growth factor (EGF), PDGF, FGF, or calcium phosphate induce an ultrastructure change within the centriole of 3T3 cells; this ultrastructural modification of the centriole is detectable by immunofluorescence within 2 h of PDGF treatment. Plasma, EGF, or MSA do not modify the centriole. SV40 induces replicative DNA synthesis in growth‐arrested 3T3 cells but does not cause this alteration in centriole structure.Gene A variants of SV40, including a mutant with temperature‐sensitive (ts) T‐antigen (ts A209), a deletion in t‐antigen (dl 884), and several ts A209 strains containing t‐antigen deletions were used to induce DNA synthesis in Balb/c‐3T3 cells. Like wild type SV40, all strains induced DNA synthesis equally well under permissive or nonpermissive conditions. Addition of PDGF or plasma had little effect on SV40‐induced DNA synthesis. Thus, the viral function that induces replicative DNA synthesis in Balb/c‐3T3 cells is not t and is not temperature sensitive. This SV40 gene function overrides the cellular requirement for hormonal growth factors. It does not induce transient centriole deciliation, a hormonally regulated event.