bluuebunny/crossref_metadata_2025 huggingface dataset:
The regional association of actin and myosin with sites of particle phagocytosis
Authors: Painter Richard G. , McIntosh Ann T.
Published: May 2005

Contractile proteins are thought to play a causative role in motile processes such as phagocytosis. In order to investigate their role in phagocytosis further, simultaneous immunofluorescence localization of F‐actin and myosin was carried out in resident mouse peritoneal macrophages after phagocytosis of opsonized zymosan particles. Both actin and myosin appeared to concentrate rapidly at sites of particle phagocytosis. The observed concentration of both proteins at such sites preceded ultimate particle engulfment. Cytochalasin B, a drug which was shown to block pseudopod extensions around the particle, did not prevent the concentration of the two contractile proteins at cell‐particle binding sites. This result ruled out path‐length effects as an explanation for the observed concentration of actin and myosin at phagocytic sites. Kinetic analysis showed that actin rapidly concentrates at particle‐cell binding sites within minutes (or less) of contact with cell surface. The two proteins are present throughout the engulfment phase until and after ingestion is complete. Finally, at later times the particles become clustered over the cell nucleus and the particle‐associated actin‐myosin seen earlier is no longer evident.
Hormone‐induced modification of EGF receptor proteolysis in the induction of EGF action
Authors: Fox C. Fred , Wrann Michael , Linsley Peter , Vale Ron
Published: May 2005

A proposal that EGF action is mediated through enhanced internalization of EGF receptors is modified to account for more recent evidence. EGF receptors turn over at a rapid rate, and the maintenance of a steady state of EGF receptors on the cell surface is provided through a rapid synthesis of EGF receptors, balancing their removal. This rapid turnover of unoccupied receptors may arise through their removal. This rapid turnover of unoccupied receptors may arise through their internalization and proteolysis in the lysosomes, in much the same way as receptors are internalized and degraded when exposed to EGF, which enhances internalization. This provides a dilemma for the endocytic activation concept, since slight enhancement of receptor internalization gives rise to a strong hormone response. This problem may be solved by the observation that EGF induces a change in its receptor, exposing an otherwise unavailable site for proteolytic cleavage. This hormone‐dependent modification of receptors may be the critical step in the induction of responses to EGF and other hormones that are internalized with their receptors. Both platelet‐derived growth factor (PDGF) and fibroblast growth factor (FGF) are shown to down‐regulate EGF receptors, though transiently, placing still more stringent requirements on the specificity by which hormones might act through endocytic activation of their receptors.
Steroid hormone receptor studies in melanoma model systems
Authors: Markland Francis S. , Horn Diane
Published: May 2005

The Transplantable B‐16 melanotic melanoma carried in syngeneic C57B1/6J female mice and the Syrian hamster melanoma cell line, RPMI 3460, were utilized to determine whether steroid‐hormone receptors are present in animal melanomas. In the B‐16 melanoma, a cytoplasmic‐estrogen receptor is detectable, but there is no evidence for androgen or progestin receptors. Some tumors contain a glucocorticoid‐binding macromolecule. Sucrosedensity gradient centrifugation of cytosol after incubation with [3H]‐estradiol revealed an 8S peak that was suppressed by excess radioinert diethylstilbesterol. Binding varied from 5–35 fmoles per mg cytosol protein. Scatchard analysis of [3H]‐estradiol binding in cytosol yielded a single class of high‐affinity binding sites; the dissociation constant is 6 × 10−10 M. The receptor molecule is shown to be estrogen‐specific by ligand competition assays. In contrast to B‐16 melanoma, no estrogen, androgen, or progestin receptor can be found in the Syrian hamster melanoma cell line. However, a substantial level of specific binding is observed using [3H]‐dexamethasone. Sucrose‐gradient centrifugation of cytosol from this cell line after incubation with [3H]‐dexamethasone revealed a 7S peak that was suppressed by excess radioinert dexamethasone. Scatchard analysis indicated a single class of high affinity sites with a dissociation constant of 2 × 10−9 M. Binding levels from 70–610 fmoles per mg cytosol protein were observed. The Syrian hamster melanoma cells also exhibit a biological response to glucocorticoids: Dexamethasone causes both an inhibition of growth and a decrease in final‐cell density in these cells.
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

The 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

A 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

In 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

A 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

One 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

Interleukin 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

The 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

The 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

Polypeptide 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

The 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

Photoaffinity 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

Medium 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

An 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

Transforming 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

We 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

We 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.
Repair of bleomycin‐damaged DNA by human fibroblasts
Authors: Hurt Myra M. , Beaudet Arthur L. , Moses Robb E.
Published: May 2005

The ability of human fibroblasts to repair bleomycin‐damaged DNA was examined in vivo. Repair of the specific lesions caused by bleomycin (BLM) was investigated in normal cell strains as well as those isolated from patients with apparent DNA repair defects. The diseases ataxia telangiectasia (AT), Bloom syndrome (BS), Cockayne syndrome (CS), Fanconi anemia (FA), and xeroderma pigmentosum (XP) were those selected for study. The method used for studying the repair of DNA after BLM exposure was alkaline sucrose gradient centrifugation. After exposure to BLM, a fall in the molecular weight of DNA was observed, and after drug removal the DNA reformed rapidly to high molecular weight. The fall in molecular weight upon exposure to BLM was observed in all cells examined with the exception of some XP strains. Prelabeled cells from some XP complementation groups were found to have a higher percentage of low molecular weight DNA on alkaline gradients than did normal cells. This prelabeled low molecular weight DNA disappeared upon exposure to BLM.
Double‐strand breaks in DNA caused by repair of damage due to ultraviolet light
Authors: Bradley Matthews O.
Published: May 2005

DNA DSBs are formed in normal human IMR‐90 cells during repair incubation after 100 and 300 J·m−2 of UVL. By contrast, no DSBs are formed after UVL in human XPA cells that are unable to excise pyrimidine dimers. The DSBs are not due to immediate cell death since all the cells excluded trypan blue at the time of assay and because XPA cells, which are much more UVL‐sensitive than IMR‐90, did not form DSBs after UVL. We suggest that these repair‐induced DSBs should be potent lesions that might lead to cytotoxicity, chromosome aberrations, deletion mutations, and perhaps cellular transformation, transformation.
The structure of fibronectin and its role in cellular adhesion
Authors: Akiyama Steven K. , Yamada Kenneth M. , Hayashi Masao
Published: May 2005

Fibronectin is a large, adhesive glycoprotein which is found in a number of locations, most notably on cell surfaces, in extracellular matrixes, and in blood. Fibronectin has been detected in all vertebrates tested and in many invertebrates. Its presence in sponges is significant because this suggests that fibronectin may have appeared very early in evolution, possibly with the most primitive multicellular organisms. Cellular and plasma fibronectins have many striking similarities. However, the locations of the polypcptide chain differences between these two proteins indicate that plasma fibronectin cannot be derived from cellular fibronectin by means of simple post‐translational proteolysis. Instead, these different types of fibronectin may be products of different genes or of differentially spliced messenger RNA molecules. Amniotic fluid fibronectin is possibly a third form of the protein. Cellular and plasma fibronectins are composed of at least six protcaseresistant domains which contain specific binding sites for actin, gelatin, heparin, Staphylococcus aureus, transglutarninase, fibrin, DNA, and a cell surface receptor. The relative locations of these domains have been mapped in the primary structure of fibronectin. The cell surface receptor for fibronectin has not been positively identified, but may be a glycoprotein, a glycolipid, or a complex of the two. Although cell‐substratum adhesion is mediated by fibronectin, the locations of the areas of closest approach of the cell to the substratum (the adhesion plaques) and fibronectin are not coincident under conditions of active cell growth. Under conditions of cell growth arrest in low scrum concentrations, some fibronectin may become localized at the adhesion plaques. Models describing the domain structure of fibronectin and the molecular organization of the adhesion plaque area are presented.
Microchemical instrumentation
Authors: Hood Leroy , Hunkapiller Michael , Hewick Rodney , Giffin Charles E. , Dreyer William J.
Published: May 2005

A number of cell surface molecules of great theoretical and practical importance simply cannot be obtained in amounts sufficient for molecular analysis using conventional methods and instrumentation. Because of our interest in such studies, we began about eight years ago to explore the possibility of developing new instrumentation for the sequence analysis of very small quantities of polypcptide chains. These efforts have led to the development of two microsequenators which employ one thousandth to one ten‐thousandth the material used in the original sequenator described by Per Edman. In addition, in conjunction with the explosion of recombinant DNA techniques, we also have begun to develop instrumentation for the sequence analysis and synthesis of DNA molecules. In this paper we describe briefly several new instruments that have been developed at Caltech. We believe this new instrumentation in conjunction with the recombinant DNA and hybridoma technologies will provide unique opportunities to analyze cell‐surface molecules in the years ahead.
Member‐associated changes during erythropoiesis. On the mechanism of maturation of reticulocytes to erythrocytes
Authors: Zweig Stephen E. , Tokuyasu K. T. , Singer S. J.
Published: May 2005

The mature mammalian erythrocyte has a unique membranoskeleton, the spectrin‐actin complex, which is responsible for many of the unusual membrane properties of the erythrocyte. Previous studies have shown that in successive stages of differentiation of the erythropoietic series leading to the mature erythrocyte there is a progressive increase in the density of spectrin associated with the membranes of these cells. An important stage of this progression occurs during the enucleation of the late erythroblast to produce the incipient reticulocyte, when all of the spectrin of the former cell is sequestered to the membrane of the reticulocyte. The reticulocyte itself, however, does not exhibit a fully formed membranoskeleton. In particular, the in vitro binding of multivalent ligands to specific membrane receptors on the reticulocyte was shown to cause a clustering of some fractions of these ligand‐receptor complexes into special mobile domains on the cell surface. These domains of clustered ligand‐receptor complexes became invaginated and endocytosed as small vesicles. By immunoelectron microscopic experiments, these invaginations and endocytosed vesicles were found to be specifically free of spectrin on their cytoplasmic surfaces.

These earlier findings then raised the possibility that the maturation of reticulocytes to mature erythrocytes in vivo might involve a progressive loss of reticulocyte membrane free of spectrin, thereby producing a still more concentrated spectrin‐actin membranoskeleton in the erythrocyte than in the reticulocyte. This proposal is tested experimentally in this paper. In vivo reticulocytes were observed in ultrathin frozen sections of spleens from rabbits rendered anemic by phenylhydrazine treatment. These sections were indirectly immunolabeled with ferritin‐antibody reagents directed to rabbit spectrin. Most reticulocytes in a section had one or more surface invaginations and one or more intra‐cellular vesicles that were devoid of spectrin labeling. The erythrocytes in the same sections did not exhibit these features, and their membranes were everywhere uniformly labeled for spectrin. Spectrin‐free surface invaginations and intracellular vesicle were also observed with reticulocytes within normal rabbit spleens. Based on these results, a scheme for membrane remodeling during reticulocyte maturation in vivo is proposed.
Factors implicated in determining the structure of zinc tubulin‐sheets: Lateral tubulin–tubulin interaction is promoted by the presence of zinc
Authors: de la Torre J. , Villasante A. , Corral J. , Avila J.
Published: May 2005

Addition of increasing amounts of zinc to a cold microtubule protein solution results in the disappearance of 30 S oligomer found in the absence of that cation and in the appearance of new tubulin oligomers, 90 S and 23 S. When a microtubule protein solution is warmed in the presence of zinc, tubulin‐sheets are assembled. We have tested the influence of microtubule associated proteins and the zinc:tubulin ratio on the polymerization process. Depletion of microtubule associated proteins results in wider and longer tubulin‐sheets than those polymerized in the presence of microtubule associated proteins. However by increasing zinc concentration wider but shorter tubulin‐sheets were found. These results suggest that microtubule associated proteins and zinc could promote nucleation of tubulin‐sheets, but zinc also promotes lateral tubulin‐tubulin interaction. This interpretation was confirmed when microtubule protein was assembled at a low zinctubulin ratio. In such conditions composite structures of microtubules and zinc tubulin‐sheets arc formed. These composite structures are consequence of a lateral attachment of a zinc tubulin‐sheet on a microtubule protofilament.
Alkylation of DNA and tissue specificity in nitrosamine carcinogenesis
Authors: Montesano Ruggero
Published: May 2005

A peculiarity of nitrosamines is the high degree of cell and organ specificity in inducing tumors. There is substantial evidence that the initiation of the carcinogenesis process by carcinogens of this group is linked to the metabolic competence of the target tissue or cell to convert these carcinogens into mutagenic metabolites and to the binding of those metabolites to cellular DNA. Alkylation occurs in the DNA at the N‐1, N‐3, and N‐7 positions of adenine; the N‐3, N‐7, and O6 of guanine; the N‐3, and O2 of cytosine; and the N‐3, O4, and O2 of thymine; and the phosphate groups. The initial proportion of each DNA adduct depends upon the alkylating agent used. The various DNA adducts are lost to a variable extent from DNA in vivo by spontaneous release of bases and Or by specific DNA repair processes. Studies conducted in vitro and in vivo indicate that alkylation at the oxygen atoms of DNA bases is more critical than alkylation at other positions in the mutagenesis and carcinogenesis induced by N‐nitroso compounds. In particular, tissues in which tumors occur more frequently after a pulse dose of nitrosamine are those in which O6‐alkylguanine persists longest in DNA, presumably resulting in an increased probability that a miscoding event (mutation) will take place during DNA synthesis. The more rapid removal of O6‐methylguanine from the DNA of liver (as compared with cxtrahepatic tissues) of rats has been associated with the absence of tumor production in this organ by a single dose of dimethylnitrosamine; however, a significant incidence of liver tumors is observed if the same dose is given 24 hr after partial hepatectomy, and tumors arc induced by such a dose of dimethyl‐nitrosamine in the liver of hamsters, which has a low capacity to remove O6‐methylguanine from its DNA. These data also indicate that the rate of disappearance of 7‐methylguanine from the liver or cxtrahepatic tissues is independent of the dose of dimethylnitrosamine; whereas O6‐methylguanine is lost from DNA more rapidly after a low dose of this nitrosamine. It has been shown that in liver the removal of O6‐methylguanine, but not of other DNA adducts, from DNA can be affected by pretreating the animals with N‐nitroso compounds. The modulation of DNA repair processes observed after a single dose and after chronic treatment with nitrosamines is discussed in relation to the tissue‐specific carcinogenic effect of this group of carcinogens.
Anomalous cell surface structure of sickle cell anemia erythrocytes as demonstrated by cell surface labeling and endo‐β‐galactosidase treatment
Authors: Fukuda Minoru , Fukuda Michiko N. , Hakomori Sen‐Itiroh , Papayannopoulou Thalia
Published: May 2005

Erythrocyte surface glycoproteins from patients with various types of sickle cell anemia have been analyzed and compared with those from normal individuals. By hemagglutination with various anti‐carbohydrate antibodies, sickle cells showed profound increase of i antigens and moderate increase of GlcNAcβ1→3Galβ1→3Glc structure, whereas antigenicity toward globosidic structure was unchanged. In parallel to these findings, erythrocytes of sickle cell patients have additional sialylatcd lactosaminoglycan in Band 3. Thus, it can be concluded that erythrocytes of sickle cell patients are characterized by an altered cell surface structure which does not appear to be due to topographical changes of cell surface membrane. It is possible that the anemia or the “stress” hematopoiesis in these patients is responsible for these changes.
Beitrag zur Entwicklung der Neoprene‐Auskleidungen zum Schutze chemischer Apparate
Authors: Tixier M.
Published: May 2005

Das Verfahren der Auskleidung von Apparaten mit vorvulkanisierten Neoprene‐Platten wird in seinen einzelnen Stufen erläutert. Anschließend werden 7 Fälle beschrieben, in denen sich diese Auskleidungen bewährt haben.
Zur Photochemie des metallischen Kupfers und deren Einfluß auf die Auflösungsgeschwindigkeit von Kupfer in Elektrolyten
Authors: Marković T. , Balaš M. , Esih I.
Published: May 2005

Durch Ätzung von Kupfer mit einem HNO3‐HCl‐Gemisch entsteht eine photoaktive Kupferschicht, die nach Belichtung eine zeitlich abhängige Schwärzung aufweist. Bei der Belichtung mit einer 6,7 V‐Glühlampe in einem Abstand von 10 cm wird auf der Kupferoberfläche ein Lichtfleck von etwa 1,75 cm2 gebildet. In bestimmten Zeitintervallen treten sodann drei Diskontinuitäten auf. Die Intensität der Reflexion wurde mit Photozelle und Spiegelgalvanometer registriert. Die Erhöhung der Temperatur führt zur Verminderung der Schwärzungsgeschwindigkeit der photoaktiven Schicht.

Die Beobachtungen über den Einfluß des Lichtes auf die Auflösungsgeschwindigkeit des Kupfers in Elektrolyten ergaben eine typische Abhängigkeit der Korrosionsgeschwindigkeit von der an der Kupfer‐Oberfläche stattgefundenen Reaktion.
Temperatur‐, wärme‐ und hitzebeständige Anstriche auf Stahl
Authors: van Oeteren K. A.
Published: May 2005

Für den Anstrich von Abgaskaminen, Öfen, Heizkörpern, Rohrleitungen für heiße Flüssigkeiten und Gase, Motore, Auspuffrohre und Gichtgasleitungen sind die normalen Anstrichmittel in der Regel unbrauchbar. Es sin daher spezielle Anstrichmittel erforderlich.

Bei der Temperaturbeanspruchung eines Anstriches ist zu unterscheiden zwischen: Höhe der Temperatur, Maximal‐ und Dauertemperatur, trockene oder feuchte Wärme, Innen‐oder Außenbeanspruchung, Temperaturwechselbeanspruchung kalt ⇌ warm, Dauer der Temperatur.

Die Temperaturbeanspruchung eines Anstriches ist daher von verschiedenen Faktoren abhängig, die erst zusammen eine Aussage gestatten. Von besonderer Bedeutung ist die Temperaturbeständigkeit des Bindemittels und der Einfluß der Pigmente, ferner die Gasdurchlässigkeit (Unterzunderung), die Ausdehnung von temperaturbeständigen Anstrichen durch thermische Einwirkung.

Vor Einsatz eines Anstrichmittels ist eine Prüfung der Temperaturbeständigkeit erforderlich. Vor Anstrich eines temperaturbelasteten Objektes ist eine Temperaturermittlung erforderlich. Die Art der Entrostung, die Anzahl der Anstriche, die Art der Anstrichtechnik und der Anstrichausführung ist bei temperaturbeanspruchten Objekten von grosser Bedeutung.
Über die Polarisationserscheinungen bei der Abscheidung von glatten Bleiüberzügen aus einem neuen, komplexen Bleiacetatbad
Authors: Machu Willibald , Lotfy Badawy M. Ali El Sayed
Published: May 2005

Die Stromdichte‐Potential‐Kurven in Lösungen von Komplexverbindungen des Bleisulfats in Bleiacetat und Ammoniumacetat lassen den Schluß zu, daß die Kornverfeinerung nicht auf eine stärkere kathodische Polarisation zurückzuführen ist. Maßgebend dafür ist vielmehr die Blockierung der aktiven Zentren an der Kathodenoberfläche. Dadurch wird das sonst vorherrschende Wachstum der Bleikristalle in Senkrechter Richtung zur Kathodenoberfläche und parallel zu den Stromlinien unterbunden. Das komplex gelöste Bleisulfat wirkt stärker kornverfeinernd als organische Zusätze im Bad.
Die Wirkung korrosiver Atmosphären auf Niederspannungsisolierungen
Authors: Sachsenweger C. , Hänsele K. , Stimper K. , Sockel H. G.
Published: May 2005

Das Isolationsverhalten elektrotechnischer Erzeugnisse wird beeinträchtigt, wenn leitfähige Korrosionsprodukte zwischen spannungsführende Elektroden gelangen. Zur zeitraffenden Simulation dienen genormte Prüfverfahren mit SO2‐ bzw. H2S‐haltigen korrosiven Atmosphären. Die Wirkung derartiger Prüfungen wurde an Prüflingen aus Al2O3‐Keramikplättchen mit gleichspannungsbeanspruchten Elektrodenpaaren aus Kupfer, Messing oder Lötzinn untersucht. Mit Hilfe von SIMS‐Analysen wurde festgestellt, daß bei H2S‐Einwirkung auf Kupfer und Messing sulfidhaltige Korrosionsprodukte in den Elektrodenzwischenraum gelangten. Vereinzelt unter SO2‐Einwirkung entstandene leitende Verbindungen zwischen Messing‐ und Lötzinnelektrodenpaaren sind demgegenüber wahrscheinlich auf vorgewachsene Metalldendriten zurückzuführen.
Werkstoff‐Datenbank
Authors: Kirchheiner R. , Kowalski (Acosta) P. , Hartung T.
Published: May 2005

Die neu entwickelte Sollwert‐Werkstoff‐Datenbank (SWDB) ist eine benutzerfreundliche Werkstoff‐Datenbank, die Informationen über genormte und nicht genormte Werkstoff‐Kennwerte massiver, metallischer Werkstoffe bereitstellt. Der Inhalt dieser Datenbank setzt sich zusammen aus Solldaten von ingenieurmäßig gebräuchlichen, massiven Werkstoffen aus Eisen‐ und Nichteisenmetallen. Neben der chemischen Zusammensetzung und den mechanisch‐technologischen Eigenschaften von metallischen Werkstoffen nach verschiedenen Normen und Spezifikationen sind eine Vielzahl möglicher alternativer Werkstoffkandidaten in kurzer, prägnanter und für den Anwender gut einsehbarer Form referiert. Die Daten sind auf der Basis eines völlig neu strukturierten Modells aufgebaut und in Abhängigkeit vom spezifizierten Werkstoff von der Erzeugnisform, der Abmessung, dem Lieferzustand und von der Probennahme wiedergegeben.

Außerdem enthält die SWDB zusätzliche Informationen über physikalische Kennwerte sowie zahlreiche Angaben zur Wärmebehandlung, Warm‐ und Kaltformgebung, Schweißbarkeit und Anwendungshinweise. Die SWDB hat eine doppelte Funktion: einerseits arbeitet sie als unabhängige Datenbank eigenständig, andererseits als Satellit‐Datenbank, die die Korrosionsfakten‐Datenbank im Informationssystem für Korrosion und Korrosionsschutz „CORIS”︁ unterstützt.
Mass spectrometry of sulfur‐containing compounds in organic and bioorganic fields
Authors: Bortolini O. , Fogagnolo M.
Published: May 2005

This survey covers the mass spectrometic properties of organosulfur compounds containing the sulfide, disulfide, and sulfone functional groups. Attention is paid to the uni‐ and biomolecular chemistry of both positive and negative ions, as well as to the reactions of ions, with sulfur containing species, in the gas phase. The role of other functional groups on the decomposition of organic S, SO, SO2 containing gaseous ions is also discussed. The selection of sulfur containing compounds includes many naturally occurring and pharmaceutically significant products, that will be presented in the following order: alkaloids, amino acids, peptides, proteins, carbohydrates, steroids, and metabolites. © 1996 John Wiley & Sons, Inc.