bluuebunny/crossref_metadata_2025_split huggingface dataset:
Endogenous and exogenous proteolysis of the acetylcholine receptor from torpedo californica
Authors: Huganir Richard L. , Racker Efraim 
Published: May 2005

AbstractPurified acetylcholine receptor reconstituted into liposomes catalyzes carbamylcholine‐dependent ion flux [10]. An endogenous protease activated by Ca2+ gives rise to an acrylamide gel pattern of the receptor with the 40,000‐dalton subunit apparently as the major component. Exogenous proteases nick the proteins so extensively that the acrylamide gel pattern reveals polypeptides of 20,000 daltons or less. In either case the receptor sediments at 9S, indicating that the polypeptide chains associated. Moreover, the nicked receptors bind α‐bungarotoxin and catalyze carbamylcholine‐dependent ion flux after reconstitution.
The selective effects of charged local anaesthetics on the glucagon‐ and fluoride‐stimulated adenylate cyclase activity of rat‐liver plasma membranes
Authors: Gordon Larry M. , Dipple Irene , Sauerheber Richard D. , Esgate Judy A. , Houslay Miles D. 
Published: May 2005

AbstractThe cationic local anaesthetics carbocaine and unpercaine were found to increase the fluoride‐stimulated adenylate cyclase up to a maximum level; above this maximum level further increases in drug concentration inhibited the enzyme. At concentrations where this activity was stimulated, a fatty acid spin label detected an increase in bilayer fluidity, which, it is suggested, is responsible for the activation of the enzyme. A solubilized enzyme was unaffected by the drugs, a finding consistent with this proposal.These cationic drugs began to inhibit the glucagon‐stimulated activity at concentrations where they activated the fluoride‐stimulated activity. It is suggested that this is due to their effect on the coupling interaction between the receptor and catalytic unit.The anionic drugs, phenobarbital, pentobarbital, and salicylic acid, all inhibited the fluoride‐stimulated enzyme. This may be due in part to a direct effect on the protein and in part to the interaction of the drugs with the bilayer. The drugs had small inhibitory effects on the lubrol‐solubilized enzyme.The glucagon‐stimulated enzyme was initially inhibited by the anionic drugs at low concentrations, then activated, and finally inhibited with increasing drug concentration. The reasons for such changes are complex, but there was no evidence from electron spin resonance studies to suggest that the elevations in activity were due to increases in bilayer fluidity.
Effects of a serum spreading factor on growth and morphology of cells in serum‐free medium
Authors: Barnes David , Wolfe Richard , Serrero Ginette , McClure Don , Sato Gordon 
Published: May 2005

AbstractA heat‐sensitive, trypsin‐sensitive factor that promoted growth and spreading of cells in serum‐free, hormone‐supplemented medium was partially purified from human serum. The major portion of the proteins in these preparations migrated upon SDS‐polyacrylamide gel electrophoresis with a mobility consistent with molecular weights between 60,000 and 90,000. The spreading activity, which we have termed serum spreading factor, stimulated growth and spreading of a wide variety of cell types. The serum spreading factor was similar to fibronectin in that it showed an affinity for the plastic cell culture substrate but was shown to be distinct from fibronectin by several criteria. This factor may prove useful in studies of cell attachment and spreading and in studies of the relationship of cell shape and cell proliferation.
Enhanced lymphoid and decreased myeloid reconstituting ability of stem cells from long‐term cultures of mouse bone marrow
Authors: Phillips R. A. 
Published: May 2005

AbstractMature, functional lymphocytes rapidly disappear from long‐term cultures of mouse bone marrow cells and never reappear. One reason for the loss of B lymphocytes is that the optimal culture conditions for maintenance of myeloid stem cells are suboptimal for lymphocyte survival. However, despite the absence of functional lymphocytes, stem cells from such cultures retain the ability to reconstitute irradiated mice with mitogen‐responsive B and T lymphocytes. In fact, in vitro grown stem cells repopulate the lymphoid system better than the myeloid system; the defective myeloid potential does not result from the absence in the cultures of Thy–1 bearing regulatory cells (TSRC). Although the cultures lack mature lymphocytes, they contain putative T cell precursors detectable with an in vitro colony‐forming assay (CFU‐T). In vitro maintenance of CFU‐T requires an appropriate adherent monolayer. Monolyaters from congenitally anemic mice of genotype S1/S1d fail to support either myeloid precursors or CFU‐T.
H1 Histone and nucleosome repeat length alterations associated with the in vitro differentiation of murine embryonal carcinoma cells to extra‐embryonic endoderm
Authors: Oshima Robert , Curiel Diana , Linney Elwood 
Published: May 2005

AbstractThe histone compositions and average distance between nucleosomes have been determined for F9.22 and PSA1 murine embryonal carcinoma cell lines, for primary extra‐embryonic endoderm derived from the in vitro differentiation of PSA1 embryonal carcinoma cells, and for two long‐term extra‐embryonic endodermal cell lines. A change in the relative proportions of two forms of the H1 histones (H1A and H1B) was found to correlate with the extra‐embryonic endodermal differentiated phenotype. The embryonal carcinoma cells had a ratio of H1A/H1B of 1.49 or greater. In contrast, extra‐embryonic endoderm from either cell lines or freshly isolated from differentiating embryonal carcinoma cell cultures had a ratio of H1A/H1B of less than 0.9. Partial peptide mapping of gel purified H1A and H1B suggest the two proteins differ in primary structure. The nucleosome repeat length of the embryonal carcinoma cell lines was 196 bp of DNA. Primary extra‐embryonic endoderm was found to have a value of 205 bp, but the long‐term extra‐embryonic endodermal cell lines had an average nucleosome repeat length of 187 bp. Since both freshly isolated primary endoderm and the long‐term endodermal cell lines express differentiated functions (basement membrane glycoproteins and plasminogen activator activity), there appears to be no simple correlation between the nucleosome repeat length and the expression of these differentiated functions.
Hybrid Ia antigens: Genetic, serologic, and biochemical analyses
Authors: Lafuse William P. , Yokota Shumpei , David Chella S. 
Published: May 2005

AbstractIa specificities 22 and 23 were found to be determinants on hybrid Ia molecules, formed by the noncovalent binding of a 26,000–28,000 dalton beta polypeptide chain (Ae) coded by the I‐A subregion and a 32,000–35,000 dalton alpha chain (Eα) coded by the I‐E subregion. For expression of Ia. 23 the Ae chain, coded by the I‐A subregion, must be derived from the H‐2d haplotype, while Ab, As, or Ak can provide the complementing beta chain for the expression of Ia. 22. For expression of Ia. 22 and Ia. 23, most Ia. 7 positive strains can provide the complementing alpha chain (Eα), with the one exception of B 10. PL (Eu), which is Ia. 7 positive but will not complement with Ad to express Ia. 23. Antisera were also produced against hybrid Ia antigens by immunizing with F1 cells expressing Ia. 22 or Ia. 23 generated by transcomplementation. These antisera detect the same specificities as conventional anti‐Ia. 22 and anti‐Ia. 23 sera produced against cis‐complementing Ia antigens. It is postulated that hybrid Ia determinants are involved in recognition and generation of immune response to antigens under dual Ir gene control. It is also suggested that there are 2 types of Ia specificities: (1) allotypic Ia specificities expressed on the alpha or beta chains (for example, Ia. 7 on the Eα chain) and (2) hybrid Ia specificities, which are unique interaction determinants formed by the association of alpha and beta chains (for example, Ia. 22 and Ia. 23). These interaction gene products may be involved in antigen recognition and presentation.
Polyclonal activation of Ts cells with antiserum directed against an IGH‐1 linked candidate for a T‐cell receptor constant region marker
Authors: Owen Frances L. 
Published: May 2005

AbstractAn anti‐T cell serum raised in allotype congenic mice recognizes the product of a new locus coding for a heavy chain‐linked polypeptide found on a subpopulation of T cells. Anti‐Tsd raised in BALB/cAnN mice against selected C.AL‐20 T cells reacts with a cell surface antigen in virgin animals that is found on 25% of mature thymocytes and Lyt‐bearing T cells, but not on prothymocytes, Lyt1 T cells or B cells. The antigen is restricted to strains bearing the Ig‐1d and Ig‐1e heavy chain allotype haplotypes, and is expressed in the F1 animal. The antigen is unlinked in expression to the Lyt2, H‐2, or kappa light chain loci. The antigen is not detected in the hematopoietic cells in the bone marrow and appears to mark only the mature peripheral pool of T cells. As previously reported, the antiserum blocks the binding of suppressor T cells to the cross‐reactive idiotype for arsonate, while reagents specific for Fab, Fc and Ig were ineffective. It seems probable that the marker may represent a T cell constant region marker analogous to the Igh products on immunoglobulin. Antiserum against this marker induces in vivo triggering of Ts cells for a wide variety of T‐dependent antigens. All subclasses of anti‐hapten antibodies are suppressed; no affinity restrictions or clonotype specificity is observed in suppressed adult mice. Results suggest that precursor T cells regulating major serum idiotypes regulate individual idiotypes.
Regulation of B lymphocyte activation by the Fc portion of immunoglobulin
Authors: Morgan Edward L. , Weigle William O. 
Published: May 2005

AbstractMurine splenic B lymphocytes are induced to proliferate and undergo polyclonal activation in the presence of Fc fragments, AHGG, antigen‐antibody complexes, and CH3 fragments derived from plasmin digestion of human Ig. The unifying feature of the polyclonal antibody response induced by these agents is that in all cases a portion of the constant region of the Ig molecule (ie, Fc region) is present. Fragments of Ig lacking the Fc piece, such as Fab and F(ab′)2 were found not to be stimulatory. In addition, a model is proposed to account for the regulatory effects of antigen‐antibody complexes on an ongoing humoral immune response.
Specific protein phosphorylation during cyclic AMP‐mediated morphological reversion of transformed cells
Authors: Bloom George S. , Lockwood Arthur H. 
Published: May 2005

AbstractTreatment of transformed Chinese hamster ovary cells with dibutyryl cAMP or other agents that elevate cAMP results in the acquisition of growth and morphology characteristic of normal fibroblasts. The role of specific protein phosphorylation in this process of morphological reversion has been examined using metabolic labelling of Chinese hamster ovary (CHO) cells with 32P‐orthophosphate in the presence or absence of N6O2′‐dibutyryladenosine 3′:5′‐cyclic monophosphoric acid (Bt2cAMP). Analysis of labelled cultures by SDS gel electrophoresis and radioautography demonstrate dramatic changes in the phosphorylation of only 2 cellular proteins during reverse transformation. A 55,000 dalton protein (pp55) was phosphorylated and a 20,000 dalton protein (pp20) was dephosphorylated. The time course of these events was consistent with the kinetics of morphological reversion. The lower molecular weight species, pp20, was dephosphorylated within 15–30 minutes, prior to all morphological changes except membrane tranquilization. The higher molecular weight protein, pp55, was maximally phosphorylated over 1–2 hours following addition of Bt2cAMP, paralleling early stages in the establishment of fibroblastic form. The phosphorylated forms of pp20 and pp55 were both extracted from cellular cytoskeletons by 0.5% Triton X‐100, but analysis of 35S‐methioninelabelled cultures suggested that unphosphorylated pp 20 may be bound to the cytoskeleton. Since pp20 was found to comigrate with the 20,000 dalton myosin light chain, it is possible that dephosphorylation of CHO cell myosin induced by cAMP may alter its interaction with actin microfilaments and modulate the assembly of stress fibers during morphological reversion.
The in vitro synthesis and processing of the branched‐chain amino acid binding proteins
Authors: Daniels Charles J. , Anderson James J. , Landick Robert , Oxender Dale L. 
Published: May 2005

AbstractThe synthesis of the leucine‐specific and LIV‐binding proteins was examined in vitro in a coupled transcription/translation system using the hybrid plasmids pOX7 and pOX13 as templates. Plasmid pOX7 contains the livK gene coding for the leucine‐specific binding protein, and pOX13 contains the liv J gene coding for the LIV‐binding protein. Both binding proteins were synthesized in vitro as precursor forms with molecular weights approximately 2,500 greater than their respective mature forms. Conversion of the precursor forms to their mature forms occurred during post‐translational incubation following synthesis in the presence of membrane. The precursor of the LIV‐binding protein was processed more rapidly than the leucine‐specific binding protein precursor. Processing activity could be removed from the in vitro synthesis system by centrifugation, suggesting that the processing activity was membrane associated. Restoration of post‐translational processing activity was achieved by adding inside‐out membrane vesicles to membrane‐depleted reaction mixtures.
Mapping the mitotic clock by phase perturbation
Authors: Klevecz R. R. , King G. A. , Shymko R. M. 
Published: May 2005

AbstractIn synchronized V79 cells perturbed by serum, heat shock, or ionizing radiation at half‐hour intervals through a modal 8.5‐hour cell cycle, phase‐response curves show a characteristic biphasic pattern of advances and delays in subsequent cell divisions. These observations, together with previous observations of quantizement of generation times in this and other cell lines have led us to consider a model incorporating, in the simplest case, a two‐component oscillator with two threshold crossings required per cell cycle. By assuming that oscillator variables respond in a simple way to the experimental perturbations, for example, by first order destruction due to heat shock, a map of the qualitative features of the oscillator can be obtained by matching simulated with experimental phase response curves. Random fluctuations in oscillator variables about a fixed trajectory lead to subthreshold oscillations and result in a distribution of generation times which is roughly a negative exponential, but quantized within this exponential envelope. The extent of the random fluctuations can be determined from comparison with data on desynchronization of a cell population after mitotic selection. The same parameters which correctly simulate phase response and the desynchronization data also give good agreement with generation time distribution data.
Cell surface receptors for endogenous mouse type C viral glycoproteins and epidermal growth factor: Tissue distribution in vivo and possible participation in specific cell‐cell interaction
Authors: Rapp U. R. , Marshall Thomas H. 
Published: May 2005

AbstractWe have described previously the detection and tissue distribution of free cell surface receptors for ecotropic R‐MuLV envelope glycoprotein and the growth factor EGF in vivo [1]. More recently, we have reported the chromosomal map position of the ecotropic viral receptor and its conservation between subspecies of the genus Mus [2]. This work has shown, for the first time, the presence of multiple, independently segregating cell surface receptor genes specific for different classes of ecotropic type C viral envelope glycoprotein. In this report we extend these findings and identify chromosome 2 as coding for the receptor used by M813, an ecotropic MuLV from a feral Asian mouse. This new receptor is probably also used by oncogenic, recombinant (MCF class) MuLV of C3H origin.
Promotion of hematopoietic stem cell differentiation in vitro by a soluble mediator, allogeneic effect factor
Authors: Altman Amnon , Gilmartin Thomas D. , Katz David H. 
Published: May 2005

AbstractThis study was designed to investigate the effects of allogeneic effect factor (AEF), a soluble mediator derived from short‐term mixed lymphocyte cultures (MLC) of in vitro alloantigen‐primed T cells, on cultures of murine bone marrow cells. Cultures established under suboptimal conditions namely, in the absence of a pre‐established adherent cell layer as required in conventional Dextertype cultures–declined and lost their stem cell activity rapidly. In contrast, supplementation of these cultures, at initiation and thereafter, with AEF, but not with T cell growth factor (TCGF), induced cell growth and proliferation for several weeks. Such AEF‐supplemented cultures exhibited cellular heterogeneity and stem cell activity for significantly longer periods than the control cultures. Even in conventional Dexter cultures, established under optimal conditions, AEF had a beneficial effect on cellular growth and proliferation and myeloid progenitor cell (CFU‐C) activity. Furthermore, cells capable of synergizing with suboptimal numbers of mature T cells in con A‐induced mitogenic responses, shown by others to be pre‐T cells, were detected in the AEF‐supplemented cultures for several weeks.
Proteolytic domains of the epidermal growth factor receptor of human placenta
Authors: O'Keefe Edward J. , Battin Teresa K. , Bennett Vann 
Published: May 2005

AbstractMicrosomal membranes from human placenta, which bind 5–20 pmol of 125I‐epidermal growth factor (EGF) per mg protein, have been affinity‐labeled with 125I‐EGF either spontaneously or with dimethylsuberimidate. Coomassie blue staining patterns on SDS polyacrylamide gels are minimally altered, and the EGF‐receptor complex appears as a specifically labeled band of 180,000 daltons which is not removed by urea, neutral buffers, or chaotropic salts but is partially extracted by mild detergents. Limited proteolysis by alpha chymotrypsin and several other serine proteases yields labeled fragments of 170,000, 130,000, 85,000, and 48,000 daltons. More facile cleavage by papain or bromelain rapidly degrades the hormone‐receptor complex to smaller labeled fragments of about 35,000 and 25,000 daltons. These fragments retain the binding site for EGF, are capable of binding EGF, and remain associated with the membrane. Alpha chymotryptic digestion of receptor solubilized by detergents yields the same fragments obtained with intact vesicles, suggesting that the fragments may represent intrinsic proteolytic domains of the receptor.
Alterations in growth requirements of kidney epithelial cells in defined medium associated with malignant transformation
Authors: Taub Mary , Ü Ben , Chuman Lorraine , Rindler Michael J. , Saier Milton H. , Sato Gordon 
Published: May 2005

AbstractThe possibility has been investigated that (1) the supplements required for the growth of the Madin Darby Canine Kidney (MDCK) cell line in serum‐free Medium K‐l are indeed requirements for the growth of normal kidney cells in vitro, and (2) that alterations in these growth requirements are associated with malignant transformation. Consistent with the hypothesis that MDCK cells resemble normal kidney cells in culture, primary cultures of baby mouse kidney epithelial cells grow in Medium K‐l and respond to the 5 components in the‐medium. The growth properties of Moloney sarcoma virus (MSV)‐transformed MDCK cells in defined media have been examined. Unlike MDCK cells, MSV‐transformed MDCK cells form tumors in adult nude mice. Although they still respond to the 5 factors in Medium K‐l, the optimal dosage for insulin is lower for the MSV transformants than for MDCK cells. The MSV transformants also have an additional requirement for growth in Medium K‐l – fibronectin. Variants of MDCK cells have been isolated that have lost the PGE1 requirement for growth in defined medium. These variant cells have acquired (1) the ability to form tumors in adult nude mice and (2) an alteration affecting cAMP metabolism, in addition to PGE1 independence.
Effect of heme on globin messenger RNA synthesis in spleen erythroid cells
Authors: Fuchs O. , Ponka P. , Borova J. , Neuwirt J. , Travnicek M. 
Published: May 2005

AbstractSynthesis of globin mRNA in erythroid spleen cells from anemic mice was measured after in vitro incubation under conditions in which the level of intracellular heme was manipulated. This newly synthesized globin mRNA was isolated by hybridization with globin cDNA covalently bound to cellulose. Isonicotinic acid hydrazide (INH) and penicillamine were used as specific inhibitors of heme synthesis. It has been found that a 120‐min incubation of spleen erythroid cells with 5 mM INH or 5mM penicillamine reduced [3H] uridine incorporation into globin mRNA by 24% or 36%, respectively. The addition of heme to INH‐ or penicillamine‐treated cells almost completely restored [3H] uridine incorporation into globin mRNA. These results indicate that heme stimulates transcription or processing of globin mRNA.
Spectrin‐4.1‐actin complex of the human erythrocyte: Molecular basis of its ability to bind cytochalasins with high‐affinity and to accelerate actin polymerization in vitro
Authors: Lin Diane Chang 
Published: May 2005

AbstractThe spectrin‐4.1‐actin complex isolated from the cytoskeleton of human erythrocyte [3] was found to be similar to muscle F‐actin in several aspects: Both the complex and F‐actin nucleate cytochalasin‐sensitive actin polymerization; both bind dihydrocytochalasin B with similar binding constants; both can be depolymerized by DNase I with loss of cytochalasin binding activity. From these results, we conclude that the actin in the complex is in an oligomeric form. However, the presence of spectrin and band 4.1 in the complex not only stabilized the actin in the complex as evidenced by its resistance to depolymerization in low‐ionic‐strength conditions and to DNase I as compared with F‐actin, but also altered the characteristics of the binding site(s) for cytochalasins believed to be located at the “barbed” (polymerizing) end of the oligomeric actin.
Effects of guanine nucleotides on cns neuropeptide receptors
Authors: Moody Terry W. , Taylor Duncan P. , Pert Candace B. 
Published: May 2005

AbstractThe effect of nucleotides on central nervous system neuropeptide receptor binding was investigated. The guanine nucleotides, guanosine‐5′‐triphosphate and guanylyl‐5′‐imidodiphosphate, significantly inhibited the binding of radiolabeled vasoactive intestinal polypeptide but not that of [Tyr4]bombesin to rat brain membranes. Vasoactive intestinal polypeptide binding was inhibited by guanine nucleotides in a dose‐dependent manner. Using a 20 μM dose, 60% of the specific vasoactive intestinal polypeptide binding was inhibited by guanylyl‐5′‐imidodiphosphate, which was more potent than guanosine‐5′‐triphosphate, whereas other nucleotides were not effective. This reduction in binding was a consequence of lower affinity of the receptor for vasoactive intestinal polypeptide, which in turn resulted from an increased rate of dissociation.