bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cloning of the histidine transport genes from salmonella typhimurium and characterization of an analogous transport system in escherichia coli
Authors: Ardeshir Feroza , Ames Giovanna Ferro‐Luzzi 
Published: May 2005

AbstractThe genes for the well‐characterized high‐affinity histidine transport system of S typhimurium have been cloned in λgt4. Genetic and physiological analyses of the analogous transport system of E coli were undertaken in order that available λ vectors, recombinant DNA techniques, and a genetic selection for transport function might be used to isolate the Salmonella genes. The presence of the transport genes on a 12.4 Kb cloned DNA fragment has been confirmed (1) genetically, by complementation studies; (2) physiologically, by the rates of histidine uptake by bacteria containing this DNA; and (3) by demonstrating that the cloned DNA codes for the previously identified transport proteins J and P. The isolated fragment carries the entire transport operon, the argT gene and the ubiX locus, but neither the purF gene nor the ack/pta loci.
Chicken tissue binding sites for a purified chicken lectin
Authors: Beyer Eric C. , Barondes Samuel H. 
Published: May 2005

AbstractA lactose‐binding lectin previously purified from embryonic chicken muscle and adult chicken liver, and here referred to as chicken‐lactose‐lectin‐I (CLL‐I), was added to sections of various adult chicken tissues to detect available binding sites. Both the sites of binding of added CLL‐I as well as the tissue distribution of endogenous CLL‐I were determined by indirect immunofluorescence using a rabbit antibody to CLL‐I followed by fluorescent goat anti‐rabbit IgG. Some tissues such as intestine and kidney showed abundant extracellular binding sites for the lectin, primarily between cells, in basement membrane, and in material on the luminal surface. In contrast, adult heart showed no significant binding sites for CLL‐I. Adult pancreas showed considerable endogenous CLL‐I in an extracellular site surrounding exocrine lobules, but added CLL‐I did not bind substantially. The distribution of CLL‐I binding sites in intestine were mimicked by those of purpurin, another lactose‐binding lectin. CLL‐I binding sites were also detected on the surface of cultured chick embryo skin fibroblasts. The factors controlling the specific distribution of occupied and unoccupied CLL‐I binding sites are not known.
The effects of laminin on the growth and differentiation of embryonal carcinoma cells in defined media
Authors: Rizzino Angie , Terranova Victor , Rohrbach David , Crowley Craig , Rizzino Heather 
Published: May 2005

AbstractIn this paper we have examined the growth and differentiation of the embryonal carcinoma cell line, F9, in the defined medium EM‐3 at low density. We show that the growth of F9 and their differentiated cells (F9‐diff) in EM‐3 is strongly density dependent. At low cell densities the growth of both cell types is severely limited and most of the cells do not survive. Although this poses a problem for working with F9 and F9‐diff in EM‐3, it provides a convenient assay for identifying molecules that support their growth at low density. Using this assay, we have determined that laminin, a newly isolated glycoprotein of basement membranes, significantly improves the growth and short‐term survival of both F9 and F9‐diff. However, addition of laminin to EM‐3 is insufficient to promote the clonal growth of these cell types. Our findings also indicate that laminin promotes the attachment of F9 and F9‐diff in defined media. On the basis of our results, we propose an attachment function for laminin during the early stages of mammalian development.
In vitro methylation of bacterial chemotaxis proteins: Characterization of protein methyltransferase activity in crude extracts of salmonella typhimurium
Authors: Clarke Steven , Sparrow Kristen , Panasenko Sharon , Koshland D. E. 
Published: May 2005

AbstractA specific in vitro assay was developed for the protein carboxyl methyltransferase that is involved in the chemotactic behaviour of Salmonella typhimurium. This cytosolic enzyme catalyzes an S‐adenosyl‐L‐methionine‐dependent methyl esterification of glutamyl residues on a class of 60,000‐dalton inner‐membrane proteins. The activity was found to display a pH optimum of 6.5 and be sensitive to the concentration of salts in the assay medium. No detectable activity was found towards a variety of other proteins which serve as substrates for mammalian and other bacterial carboxyl methyltransferases. This assay was used to quantitate the methylation of the 60,000‐dalton methyl‐accepting proteins in response to chemoeffectors. Small but reproducible concentration‐dependent changes in the initial rates of in vitro methylation were observed with chemotactic attractants and repellents. The specific methyltransferase activity was found to be absent in several mutants in flagellar synthesis (fla−), suggesting that the synthesis of this enzyme is coordinately regulated with that of flagellin and basal bodies. The hydrodynamic properties of the enzyme in crude extracts were determined by gel filtration and sucrose velocity gradient centrifugation, and a native molecular weight of 41,000 was calculated from these data.
Evolution of membrane bioenergetics
Authors: Wilson T. Hastings , Lin Edmund C. C. 
Published: May 2005

AbstractOne of the first problems encountered by primitive cells was that of volume regulation; the continuous entry of ions, (eg, NaCl) and water in response to the internal colloid osmotic pressure threatening to destroy the cell by lysis. We propose that to meet this environmental challenge cells evolved an ATP‐driven proton extrusion system plus a membrane carrier that would exchange external protons with internal Na+. With the appearance of the ability to generate proton gradients, additional mechanisms to harness this source of energy emerged. These would include proton‐nutrient cotransport, K+ accumulation, nucleic acid entry, and motility. A more efficient system for the uptake of certain carbohydrates by vectorial phosphorylation via the PEP‐phosphotransferase system probably appeared rather early in the evolution of anaerobic bacteria.The reversal of the proton‐ATPase reaction to give net ATP synthesis became possible with the development of other types of efficient proton transporting machinery. Either light‐driven bacterial rhodopsin or a redox system coupled to proton translocation would have served this function. Oxidation of one substrate coupled to the reduction of another substrate by membrane‐bound enzymes evolved in such a manner that protons were extruded from the cell during the reaction. The progressive elaboration of this type of redox proton pump permitted the use of exogenous electron acceptors, such as fumarate, sulfate, and nitrate. The stepwise growth of these electron transport chains required the accretion of several flavoproteins, iron‐sulfur proteins, quinones, and cytochromes. With modifications of these four basic components a chlorophyll‐dependent photosynthetic system was subsequently evolved. The oxygen that was generated by this photosynthetic system from water would eventually accumulate in the atmosphere of the earth. With molecular oxygen present, the emergence of cytochrome oxidase would complete the respiratory chain.The proton economy of membrane energetics has been retained by most present‐day microorganisms, mitochondria, chloroplasts, and cells of higher plants. A secondary use of the energy stored as an electrochemical difference of Na+ for powering membrane events probably also evolved in microorganisms. The exclusive use of the Na+ economy is distinctive of the plasma membrane of animal cells; the Na+‐K+ ATPase sets up an electrochemical Na+ gradient that provides the energy for osmoregulation, Na+‐nutrient cotransport, and the action potential of excitable cells.
Purification of human interleukin 1
Authors: Lachman Lawrence B. , Page Stella O. , Metzgar Richard S. 
Published: May 2005

AbstractInterleukin I (IL‐1) is a lymphocyte stimulant released by human monocytes cultured for 18–24 hours in tissue culture medium containing 5% serum and the non‐specific immunostimulant lipopolysaccharide (LPS). Human IL‐1 is found in the conditioned medium in a low molecular weight (∼ 13,000) and a high molecular weight (∼ 85,000) form. The high MW activity may result from the formation of a complex between IL‐1 and serum constituents. During the course of purification, the low MW IL‐1 activity is often recovered in a high MW form. Hollow fiber diafiltration and membrane ultrafiltration has been found to rapidly separate low MW IL‐1 from all measurable protein with a yield of 4% of the original activity. The IL‐1 which converts to the high MW form during the purification is recoverable, 21% of the original activity, but contains small amounts of serum proteins. Isoelectric focusing (IEF) of the low MW IL‐1 resulted in a very highly purified sample which was analyzed by polyacrylamide gel electrophoresis (PAGE). Utilizing a new staining procedure which detects less than 1 ng of protein per band, the IEF‐purified IL‐1 revealed trace quantities ( < 1 ng) of a slowly migrating protein similar to immunoglobulin and no other bands. There were no bands which corresponded with the known electrophoretic mobility of IL‐1. Since the samples applied to the gel contained significant biological activity, this result implies that human IL‐1 is biologically active in picogram quantities.
Characterization of monolayer and organ cultures of cloned and enriched lymphohematopoietic stromal cell populations
Authors: Anderson R. W. , Sharp J. G. 
Published: May 2005

AbstractThe role of hematopoietic microenvironments in the regulation of maturation and differentiation of hematopoietic cells, although heavily debated, remains uncertain. Several investigators have suggested that the adherent “stromal” cell populations, which grow as colonies in cultures of lymphomyeloid tissues, include the cells involved in such regulatory processes. Grossly, the colonies described by several investigators appear similar morphologically, and the cells giving rise to them have been variously termed (1) fibroblast colony forming cells (FCFC), (2) plaque forming units‐culture (PFU‐C), (3) macrophage colonies, and (4) marrow stromal cells. FCFC have been reported to re‐establish their parent microenvironment when transplanted in an allogeneic system. In this study, cloned and enriched cell populations obtained from such colonies in cultures of murine lymphomyeloid tissues have been characterized by their growth in culture and using morphological, histochemical, and electron microscopic techniques. The results demonstrated that, although the initial stromal colonies appeared to be identical, the constituent cell types varied considerably. Some colonies were comprised primarily of macrophages, while others appeared to contain predominantly fibroblasts; two additional cell types that established colonies have not yet been satisfactorily identified. These results demonstrate the heterogeneity of lymphomyeloid stromal colonies. There is a need for caution in the analysis of experiments in which uncharacterized stromal cell colonies are transplanted or employed as supporting monolayers in culture systems in experiments designed to evaluate the origins and functions of lymphohematopoietic stroma.
Regulation of muscarinic receptor binding by guanine nucleotides and N‐ethylmaleimide
Authors: Ehlert Frederick J. , Roeske William R. , Yamamura Henry I. 
Published: May 2005

AbstractThe regulation of muscarinic receptor binding by guanine nucleotides and N‐ethylmaleimide (NEM) was investigated using the agonist ligand, [3H] cis methyldioxolane ([3H] CD). Characterization studies on rat forebrain homogenates showed that [3H] CD binding was linear with tissue concentration and was unaffected by a change in pH from 5.5 to 8.0. The regional variation in [3H] CD binding in the rat brain correlated generally with [3H] (−)3‐quinuclidinyl benzilate ([3H] (−)QNB) binding, although the absolute variation in binding was somewhat less. At a concentration of 100 μM, the GTP analogue, guanyl‐5′‐yl imidodiphosphate [Gpp(NH)p], caused a 43–77% inhibition of [3H] CD binding in the corpus striatum, ileum, and heart. The results of binding studies using several Gpp(NH)p concentrations demonstrated that the potency of this guanine nucleotide for inhibition of [3H] CD binding was greater in the heart than in the ileum. In contrast to its effects on [3H] CD binding, Gpp(NH)p caused an increase in [3H] (−)QNB binding in the heart heart and ileum and no change in [3H] (−)QNB binding in the corpus striatum. When measured by competitive inhibition of [3H] (−)QNB binding to the longitudinal muscle of the ileum, Gpp(NH)p (100 μM) caused an increase in the IC50 values of a series of agonists in a manner that was correlated with the efficacy of these compounds. The results of binding studies on NEM treated forebrain homogenates revealed an enhancement of [3H] CD binding by NEM.
Polypeptide growth factors: Some structural and mechanistic considerations
Authors: Bradshaw Ralph A. , Rubin Jeffrey S. 
Published: May 2005

AbstractPolypeptide growth factors are substances that stimulate an increase in cell size and/or cell number during embryonic development. In some cases, they have a similar effect on tissues in the mature organism where they function as “maintenance” factors to sustain cell viability. While their profound impact on cell behavior is well recognized, their relationship to other regulators of cell function has remained generally ill‐defined. However, the developing appreciation of their hormone‐like behavior suggests that they may be conveniently grouped with many other endocrine agents to form a broader group of secondary hormones. The utility of the classification is illustrated by the insulin‐related family of molecules. It also serves to emphasize the similarities in function shared by many of these substances including trophic stimulation and modulation of gene expression. Internalization, though, appears to be another common feature. However, whether the uptake of the growth factor mediates an intracellular action or is designed solely to regulate responsiveness at the cell surface and/or degradation remains an important unanswered question. A brief review of two growth factors (nerve growth factor and epidermal growth factor) serves to outline the possible functions that may be served by this endocytotic process.
Plate‐Induced tumors of BALB/3T3 cells exhibiting foci of differentiation into pericytes, chondrocytes, and fibroblasts
Authors: Boone Charles W. , Scott Robert E. 
Published: May 2005

AbstractThe BALB/3T3 clone A31 mouse embryo cell line has been used by many investigators as a model “normal” “fibroblast” line for a variety of in vitro studies. It has been shown, however, that these cells are not “normal” because they will produce tumors within 2–4 months if 3 × 104 cells are implanted subcutaneously in BALB/c mice attached to 0.2 × 5 × 10‐mm plastic plates. Previous studies also suggested that these cells were not fibroblasts because they gave rise to tumors with the characteristics of vascular endothelium not fibroblasts. We now report that BALB/3T3 (clone A31), BALB/3T3‐T, a proadipocyte subclone of clone A31 cells, and six recent subclones of BALB/3T3‐T cells show additional differentiation patterns when tumors derived by implantation of these cells attached to plastic plates are examined. Differentiation into pericytes, chondrocytes, and fibroblasts was observed. We conclude that the BALB/3T3 clone A31 cell line and related lines are multipotent mesenchymal cells which are capable of differentiation into a variety of cell types.
Photoaffinity labeling of the insulin receptor in H4 hepatoma cells: Lack of cellular receptor processing
Authors: Hofmann Cecilia , Ji Tae H. , Miller Bonnie , Steiner Donald F. 
Published: May 2005

AbstractPhotoaffinity labeling techniques were used to identify insulin‐binding components of the plasma membrane in insulin‐responsive, monolayer‐cultured hepatoma cells. The activated, photosensitive reagent, an n‐hydroxysuccinimide ester of 4‐azidobenzoic acid, was coupled with highly purifed insulin, and the hormone derivative was subsequently iodinated, bound to cell surface receptors of intact H4 cells, and photoactivatcd. After dissolution of the cells, labeled proteins were analyzed by SDS/polyacrylamide gel electrophoresis under reducing conditions. The main labeled band exhibited an apparent molecular weight of 130,000. Two minor components of apparent mol wt 95,000 and 40,000 were also identified. Specific labeling of all 3 bands was inhibited by simultaneous incubation of the cells with native insulin, but not by the heterologous hormone, glucagon, prior to photoactivation. Binding of azidobenzoyl‐insulin to H4 cells was time‐dependent, as was the correlated labeling of receptor components. Band‐labeling by the photosensitive insulin derivative was totally light‐dependent; spontaneous covalent linking of insulin and receptor was not observed. The labeled receptor‐related proteins were not degraded by the cells under our experimental conditions.
Stimulatory activity of PHA‐LCM for normal human hemopoietic progenitors and leukemic blast cell precursors: Separation by isoelectric focusing
Authors: Fauser A. A. , Messner H. A. 
Published: May 2005

AbstractMedium conditioned by leukocytes in the presence of phytohemagglutinin (PHA‐LCM) promotes growth of human hemopoietic progenitors (CFU‐GEMM, BFU‐E, CFU‐C) and precursors of leukemic blast cells. PHA‐LCM was separated by isoelectric focusing and each fraction tested with nonadherent cells of normal individuals as well as blast cells from two patients with acute myelogenous leukemia. Activity profiles for CFU‐GEMM, BFU‐E and CFU‐C ranged from pH 5.0–6.5. The profile for activity stimulatory for leukemic blast cells was broader and ranged from pH 5.5–7.5. Although some overlap was observed, the main peaks of stimulatory activity for normally differentiating progenitors and precursors of leukemic blast cells were separable with respect to their isoelectric point.
Release of erythropoietin from macrophages by treatment with silica
Authors: Rich I. N. , Anselstetter V. , Heit W. , Zanjani E. , Kubanek B. 
Published: May 2005

AbstractAn erythropoietic stimulating factor (ESF) can be shown to be released from preincubated macrophage‐containing cell suspensions from mice by the macrophage‐specific, cytotoxic agent, silica. A concentrated silica treated spleen cell supernatant containing ESF is shown to cause a dose dependent increase in 59 Fe incorporation into red blood cells using the in vivo polycythemic mouse bioassay. The ESF from the same supernatant can also be neutralized by anti‐erythropoietin. A second concentrated supernatant fractionated using wheat germ lectin‐Sepharose 6MB and compared to either unfractionated or fractionated step 111 erythropoietin (Ep), tested in vitro using the erythroid colony‐forming technique and 12‐day fetal liver as target cells, indicates parallelism of all linear dose‐response lines. This, together with the in vivo data, strongly suggests that the ESF released from macrophages treated with silica is, in fact, Ep. Substituting Ca2+ ions for fetal calf serum in the preincubation procedure results in the same activity being released compared to the presence of 1% or 20% fetal calf serum.
Transforming growth factors (TGFs): Properties and possible mechanisms of action
Authors: Todaro George J. , De Larco Joseph E. , Fryling Charlotte , Johnson Patricia A. , Sporn Michael B. 
Published: May 2005

AbstractTransforming growth factors (TGFs) are growth‐promoting polypeptides that cause phenotypic transformation and anchorage‐independent growth of normal cells. They have been isolated from several human and animal carcinoma and sarcoma cells. One TGF is sarcoma growth factor (SGF) which is released hy murine sarcoma virus‐transformed cells. The TGFs interact with epidermal growth factor (EGF) cell membrane receptors. TGFs are not detectable in culture fluids from cells which contain high numbers of free EGF cell membrane receptors. SGF acts as a tumor promoter in cell culture systems and its effect on the transformed phenotype is blocked by retinoids (vitamin A and synthetic analogs). The production of TGFs by transformed cells and the responses of normal cells to the addition of TGFs to the culture medium raise the possibility that cells “autostimulate” their own growth by releasing factors that rebind at the cell surface. The term “autocrine secretion” has been proposed for this type of situation where a cell secretes a hormone‐like substance for which it has external cell membrane receptors. The autocrine concept may provide a partial explanation for some aspects of tumor cell progression.
Phenotypic diversification of a cultured tumor line as a function of substratum
Authors: Dugan Charles B. , Macario Alberto J. L. 
Published: May 2005

AbstractWe have found that a murine hepatoma displays a considerable phenotypic diversification in culture, which depends upon the substratum utilized, and is manifested by the formation of multicellular structures of differing geometry: Monolayer on glass and plastic, thick multilayer pads on Gelfilm, and spheroids on agar and agarose. These multicellular morphological phenotypes were assayed without disruption to ascertain their antigenicity in vitro and their tumorigenicity in vivo and to obtain quantitative information on the effect of the spatial arrangement of the hepatoma cells upon the ability of each multicellular structure to interact, as a whole, with molecules and cells in its surroundings.The antigenicity of the multicellular structures was determined with calibrated probes and a methodology that measures the total antigenicity, as well as antigenicity per unit of surface area. Antigenicity was found to differ in the following decreasing order: Monolayer on plastic > spheroids on agarose > spheroids on agar > multilayer on Gelfilm. At least part of these antigenic variants arise from different degrees of masking of the structures' surface determinants by a trypsin‐sensitive material.The multicellular phenotypes also differed in tumorigenicity. When assayed in syngeneic hosts under comparable conditions, agar‐grown spheroids produced the fewest tumors, whereas Gelfilm‐grown multilayers produced the most.These two independent sets of data show that the various geometries that a tumor tissue is induced to acquire by the culture substratum are accompanied by a distinctive combination of surface and biological properties.
Sperm–egg binding: Identification of a species‐specific sperm receptor from eggs of strongylocentrotus purpuratus
Authors: Rossignol Daniel P. , Roschelle Aimee J. , Lennarz William J. 
Published: May 2005

AbstractWe have attempted to identify a surface component of echinoderm eggs that is involved in the species‐specific binding of sperm. Cell surface membranes from eggs of the sea urchins Strongylocentrotus purpuratus or Arbacia punctulata were radioiodinated, detergent‐treated, and subjected to density‐gradient centrifugation. In the presence of bindin, the complementary binding protein isolated from sperm, one component of the membranes sedimented to a different density. This membrane component bound‐species specifically to sperm that had undergone the acrosome reaction. This binding led to an inhibition of the ability of treated sperm to fertilize eggs. Exhaustive proteolytic digestion of this receptor fraction yields a high molecular weight glycopeptide that can also bind to bindin. It therefore appears that this egg surface membrane fraction contains a functionally intact, species‐specific receptor for sperm.