bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of membrane morphogenesis in bacteriophage PM2
Authors: Brewer Gregory J. 
Published: May 2005

AbstractThe regulation of membrane formation in bacteriophage PM2 serves as a simple model for changes in membrane structure in eukaryotic cells. Prior to Pseudomonas host lysis, wild‐type virions mature to an icosahedral morphology at the inner face of the cytoplasmic membrane. The proliminary charcterization of two temperature‐sensitive mutants of PM2 is described.In cells infected at the restrictive temperature with ts 1, an abundance of “empty” virus‐size membrane vesicles are seen. Synthesis of DNA is also reduced in ts 1 infected cells. The preponderance of vesicles is not sen in cells infected with wil‐type virus or with ts 1 at the permissive temperature. The “empty” appearance of the viral membranes suggests that viral DNA is not encapsulated.The major viral capsid protein (MW 26,000) is located just out side the viral membrane and normallyl sediments with host and virus membranes; insted, large amounts of capsid protein can be precipitated from the supernatant with TCA. Compared to cells infected with wild type virus, cells infected with is 5 at th restrictive temperature produce inside the cell an aboundance of virus‐soze membrane vesicles.Taken Together, These results with viral mutants suggest that formation of a viral membrane of the proper size does not require a DNA core around which to form, or an outer scaffolding of coat protein against which to form a spherical bilayer.
Immunospecific labeling of mouse lymphocytes in the scanning electron microscope
Authors: Carter David P. , Wofsy Leon 
Published: May 2005

AbstractBone marrow‐derived (B) and thymus‐derived (T) Balb/c mouse lymphocytes were identified in the scanning electron microscope (SEM) by the immunospecific attachment of one of several kinds of large‐molecular‐weight markers distinguishable in SEM. These markers (tobacco mosaic virus, keyhole limpet hemocyanin, bushy stunt virus, and bacteriophage T4) could be modified with hapten groups and linked with anti‐hapten antibody, in an indirect (sandwich) scheme, to hapten‐modified anti‐cell‐surface antibody bound to the cell surface.Hapten‐modified antibodies to B cell antigens (goat anti‐mouse‐immunoglobulin) or to T cell antigens (rabbit anti‐mouse brain) were employed to identify these two lymphoid cell types in unfractionated spleen, mesenteric lymph node, bone marrow, and thymus cell populations. The topography of B cells was always indistinguishable from that of T cells. No surface features were found to be unique to either cell type. In suspension, the majority of B and T cells had one or no microvilli regardless of the tissue source of the labeled cells. Cells in suspension that had microvilli (usually 10% of the total cell population) were always unlabeled. However, after cell contact with a glass surface, approximately half of both the B and T cell populations had a villous topography.
Cyclic nucleotides, thioldisulfide status of proteins, and cellular control processes
Authors: Rebhun Lionel I. , Miller Marcia , Schnaitman Terry C. , Nath Jayasree , Mellon Margaret 
Published: May 2005

AbstractIt is shown that cyclic nucleotides can have a variety of effects on cell division, cell shape, cell adhesion, and cell movement, depending on the cells selected and the conditions under which they are used. For example, while CHO cells elongate under the influence of exogenous dibutyryl CAMP, Y‐1 adrenal tumor cells round up and polyoma‐transformed 3T3 cells show no change in shape. The totality of experience with cyclic nucleotides suggests that where they have been used by cells as control elements involving the four processes listed above, they are superimposed on basic cellular processes that progress in their absence – that is, they must be acting indirectly. In attempting to understand the inhibitory action of methyl xanthines on egg development, we were forced to abandon the idea that they acted through cyclic nucleotides. We found that methyl xanthines inhibited the activation of glutathione reductase and that glutathione oxidizing agents act as mitotic inhibitors. Further, we found that tubulin polymerizability, NAD‐kinase activity, and a mitotic apparatus associated Ca+2‐ATP‐ase were all inhibited by oxidation of some of their sulfhydryls and were activated by reduction of the resulting disulfides. These results are discussed in terms of reported cycles and activations of glutathione reductase (GR) in cells and reports that mixed disulfides of glutathione and proteins can act as substrates for GR. Using the fact that a CAMP‐dependent protein kinase has been reported to be activated by glutathione, we have suggested potential sites where sulfhydryl control processes and cyclic nucleotide control processes may interact in certain restricted cases.
Cell shape and hexose transport in normal and virus‐transformed cells in culture
Authors: Bissell Mina J. , Farson Deborah , Tung Agatha S. C. 
Published: May 2005

AbstractThe rate of hexose transport was compared in normal and virus‐transformed cells on a monolayer and in suspension. It was shown that: (1) Both trypsin‐removed cells and those suspended for an additional day in methyl cellulose had decreased rates of transport and lower available water space when compared with cells on a monolayer. Thus, cell shape affects the overall rate of hexose transport, especially at higher sugar concentrations. (2) Even in suspension, the initial transport rates remained higher in transformed cells with reference to normal cells. Scanning electron micrographs of normal and transformed chick cells revealed morphological differences only in the flat state. This indicates that the increased rate of hexose transport after transformation is not due to a difference in the shape of these cells on a monolayer.
A comparison of the effects of gentle heating, acetone, and the sulfhydryl reagent bis (4‐fluoro‐3‐nitrophenyl) sulfone on the ATPase activity and pellet height response of tetrahymena cilia
Authors: Blum J. J. , Hayes A. 
Published: May 2005

AbstractIncubation of glycerol‐extracted, Triton X‐100 demembranated Tetrahymena cilia with 2–10 vol % acetone caused an enhancement of ATPase activity by 2‐ to 3‐ fold, depending on concentration and time of incubation. Axonemal ATPase activity was also increased upon incubation with bis (4‐fluoro‐3‐nitrophenyl) sulfone (FNS). Acetone and FNS enhanced the activity of solubilized 30S dynein, but slightly inhibited that of 14S dynein. Heating at 38°C, incubation with FNS, and incubation with acetone activated axonemal ATPase to the same extent. Subsequent studies of (1) the effect of time of preincubation with a spin‐labeled maleimide (SLM) at 25°C as a function of pH on the ATPase activity, (2) the concentration dependence of the inhibition of ATPase activity by N‐ethylmaleimide or SLM, (3) the ratio of ATPase activity assayed at 25°C to that assayed at 0°C, and (4) the ratio of ATPase activity at pH 8.6 to that at pH 6.9 did not reveal any difference in the properties of the axonemal ATPase after near maximal enhancement by the heat, acetone, or FNS treatments. It was concluded that enhancement of ATPase activity by gentle heat treatment, by incubation with acetone (or other organic solvents), or by FNS results from a conformation change of 30S dynein.The effect of acetone and of FNS on the pellet height response (a measure of the increase in height of the pellet of cilia precipitated by brief centrifugation in the presence of ATP as compared to the absence of ATP) was also determined. Enhancement of ATPase by these reagents did not lead to a decrease in pellet height response. This observation, in conjunction with other data, indicates that there are at least 3 states of the cross‐bridge cycle of dynein arms in cilia.
Conformation and intermolecular interactions of carbohydrate chains
Authors: Morris Edwin R. , Rees David A. , Thom David , Welsh E. Jane 
Published: May 2005

AbstractFor consideration of their conformations and interactions, carbohydrate chains can conveniently be divided into 3 classes on the basis of their covalent structure; namely periodic (a), interrupted periodic (b), and aperiodic (c) types. In aqueous solution carbohydrate chains often exist as highly disordered random coils. Under appropriate conditions, however, polysaccharides of types (a) and (b) can adopt a variety of ordered conformations. Physical methods, and in particular optical rotation, circular dichroism, and nuclear magnetic resonance, provide sensitive probes for the study of the mechanism and specificity of these disorder‐order transitions in aqueous solution.Intermolecular interactions between such polysaccharide chains arise from co‐operative associations of long structurally regular regions which adopt the ordered conformations. For acidic polysaccharides these cooperative associations may involve alignment of extended ribbons with cations sandwhiched between them. In other systems the interactions involve double belices which may then aggregate further, and geometric “matching” of different polysaccharide chains can also occur. These ordered, associated regions are generally terminated by deviations from structural regularity or by “kinks” which prevent complete aggregation of the molecules.The complex carbohydrate chains which occur at the periphery of animal cells have very different, aperiodic structures and although their conformations are as yet poorly understood, preliminary indications are considered.
The sialoglycoprotein subunits of human placental brush border membranes characterized by two‐dimensional electrophoresis
Authors: Wada H. Garrett , Góarnicki Stella Z. , Sussman Howard H. 
Published: May 2005

AbstractA brush border membrane enriched fraction was isolated from human, full‐term placenta. This membrane fraction exhibited large membrane fragments with microvilli projecting from the basal membrane in electron micrographs and was enriched tenfold in alkaline phosphatase, a brush border enzyme marker. The sialoglycoproteins associated with this membrane fraction were tritiated by mild periodate oxidation of sialic acid and reduction with tritiated NaBH4. The membranes were solubilized in 8 M urea, 2% Triton X‐100, and the tritiated glycoprotein subunits were reduced with β‐mercaptoethanol and characterized by 2‐dimensional polyacrylamide gel electrophoresis using a method similar to that described by O'Farrell and Bhakdi, Knüferman, and Wallach. The tritiated subunits were detected in the gels by autofluorography. The 2‐dimensional subunit “maps” resolved at least 17 major sialoglycoprotein subunits whereas only 10 major periodate‐Schiff reagent staining components were resolved by 1‐dimensional SDS polyacrylamide gel electrophoresis. Placental alkaline phosphatase (PAP) was identified on the subunit maps by inclusion of 32P‐labeled PAP in the tritiated membrane sample. The 32P‐labeled PAP corresponded to a major tritiated sialoglycoprotein subunit, which was heterogeneous with respect to charge as demonstrated by 3 closely running spots of the same molecular weight.
Hexose transport regulation in cultured hamster cells
Authors: Christopher C. William 
Published: May 2005

AbstractHamster (nil) cells maintained overnight in culture medium containing cycloheximide and either glucose or fructose exhibit strikingly different rates of hexose transport and metabolism (i.e., uptake). Pretreatment of cultures with sulfhydryl reagents makes it possible to determine initial transport rates for a physiological sugar such as galactose which is a catabolite in hamster cells. Using galactose transport as a model, hexose uptake enhancements can now be shown to be due almost entirely to increase in the rate of the transport step. The transport regulation can best be accounted for by a model comprised of 2 antagonizing mechanisms. This model involves turnover of transport carriers as well as inhibitory units (“regulators”). The experimental as well as the theoretical model may also apply to the well‐known uptake enhancements observed in oncogenically transformed cells.
High‐affinity phlorizin binding to brush border membranes from small intestine: Identity with (a part of) the glucose transport system, dependence on the Na+‐gradient, partial purification
Authors: Tannenbaum Carl , Toggenburger Gerhard , Kessler Markus , Rothstein Aser , Semenza Giorgio 
Published: May 2005

AbstractIn the presence of an NaSCN gradient phlorizin binds with a high affinity (Kd ⋍ 4.7 μM) to vesicles derived from brush border membranes of intestinal cells of rabbits. The value for Kd corresponds closely to that of Ki determined from phlorizin inhibition of sugar transport. The apparent affinity for phlorizin is decreased if NaCl is substituted for NaSCN and decreased substantially if the gradient of NaSCN is allowed to dissipate prior to the phlorizin binding. The number of high affinity binding sites is about 11 pmol/mg protein. Additional binding to low affinity sites can amount to as much as 600 pmol/mg protein after prolonged exposure to phlorizin (5 min). The high affinity sites are related to glucose transport based on the similarity of the Kd and Ki values under a variety of conditions and on the inhibition of the binding by D‐glucose but not by D‐fructose. The transport system and the high affinity phlorizin binding sites can be enriched by a factor of 2–3 by treatment of vesicles with papain, which does not affect the transport system, but considerably hydrolyzes nonrelevant protein.
The amino‐ and carboxyl‐terminal sequence of bovine rhodopsin
Authors: Hargrave Paul A. , Fong Shao‐Ling 
Published: May 2005

AbstractThe amino terminus of bovine rhodopsin is blocked and has the sequence x‐Met‐Asn(CHO)‐Gly‐Thr‐Glu‐Gly‐Pro‐Asn‐Phe‐Tyr‐Val‐Pro‐Phe‐Ser‐Asn(CHO)‐Lys‐Thr‐Gly‐Val‐Val‐Arg, where CHO represents sites of carbohydrate attachment. The carboxyl‐terminal sequence of rhodopsin is Val‐Ser‐Lys‐Thr‐Glu‐Thr‐Ser‐Gln‐Val‐Ala‐Pro‐Ala. Upon short‐term digestion of rod outer segment (ROS) membranes with thermolysin, opsin (∼ 35,000 daltons) is converted to a membrane‐bound fragment O′ (∼ 30,500 daltons) and 2 peptides containing 12 amino acids are released from the carboxyl terminus of rhodopsin into the supernatant. Upon long‐term digestion of ROS with thermolysin, opsin and O′ are replaced by the membrane‐bound fragments F1 (∼25,000 daltons), and F2 (∼9,500 daltons). When 32P‐ROS are digested, F2 carries the 32P. Both O′ and F1 contain the amino‐terminal glycopeptide.
Kinetics of Na+‐dependent D‐glucose transport
Authors: Hopfer Ulrich 
Published: May 2005

AbstractThe kinetic parameters of the Na+‐dependent glucose transport system have been determined in isolated membrane vesicles for D‐glucose, Na+, and phlorhizin. The D‐glucose flux measurements were carried out by the equilibrium exchange procedure at constant external and internal Na+ concentrations and zero potential. Equations were developed to extract information about Km and Vmax from uptake measurements into a vesicle population that is heterogeneous with respect to size (surface to volume ratio). The Km for D‐glucose was 14 mM and independent of the Na+‐concentration, while the Vmax was strongly Na+‐dependent and increased 15‐fold between 1 and 100 mM Na+. The Km of Na+ for activation of the Vmax was 18 mM. The calculated KI values for phlorhizin were 2.7 and 1.9 μM when determined under active and equilibrating D‐glucose flux conditions, respectively.
Orientation of the protonmotive force in membrane vesicles of escherichia coli
Authors: Adler Lawrence W. , Ichikawa Tomio , Hasan Syed M. , Tsuchiya Tomofusa , Rosen Barry P. 
Published: May 2005

AbstractMembrane vesicles of Escherichia coli can be produced by 2 different methods: lysis of intact cells by passage through a French pressure cell or by osmotic rupturing of spheroplasts. The membrane of vesicles produced by the former method is everted relative to the orientation of the inner membrane in vivo. Using NADH, D‐lactate, reduced phenazine methosulfate, or ATP these vesicles produce protonmotive forces, acid and positive inside, as determined using flow dialysis to measured the distribution of the weak base methylamine and the lipophilic anion thiocyanate. The vesicles accumulate calcium using the same energy sources, most likely by a calcium/proton antiport. Calcium accumulation, therefore, is presumably indicative of a proton gradient, acid inside.The latter type of vesicle, on the other hand, exhibits D‐lactate‐dependent proline transport but does not accumulate calcium with D‐lactate as an energy source. NADH oxidation or ATP hydrolysis, however, will drive the transport of calcium but not proline in these vesicles. Oxidation of NADH or hydrolysis of ATP simultaneous with oxidation of D‐lactate does not result in either calcium or proline transport. These results suggest that the vesicles are a patchwork or mosiac, in which certain enzyme complexes have an orientation opposite to that found in vivo, resulting in the formation of electrochemical proton gradients with an orientation opposite to that found in the intact cell. Other complexes retain their original orientation, making it possible to set up simultaneous proton fluxes in both directions, causing an apparent uncoupling of energy‐linked processes. That the vesicles are capable of generating protonmotive forces of the opposite polarity was demonstrated by measurements of the distribution of acetate and methylamine (to measure the ΔpH) and thiocyanate (to measure the Δψ).
Involvement of membrane sulfhydryls in the activation and maintenance of nutrient transport in chick embryo fibroblasts
Authors: Smith‐Johannsen H. , Perdue J. F. , Ramjeesingh M. , Kahlenberg A. 
Published: May 2005

AbstractAt 5 μg/ml, insulin stimulates hexose, A‐system amino acid, and nucleoside transport by serum‐starved chick embryo fibroblasts (CEF). This stimulation, although variable, is comparable to that induced by 4% serum. The sulfhydryl oxidants diamide (1–20 μM). hydrogen peroxide (500 μM), and methylene blue (50 μM) mimic the effect of insulin in CEF.PCMB‐S,1 a sulfhydryl‐reacting compound which penetrates the membrane slowly, has a complex effect on nutrient transport in serum‐ and glucose‐starved CEF. Hexose uptake is inhibited by 0.1–1 mM PCMB‐S in a time‐ and concentration‐dependent manner, whereas A‐system amino acid transport is inhibited maximally within 10 min of incubation and approaches control rates after 60 min. A differential sensitivity of CEF transport systems is also seen in cells exposed to membrane‐impermeant glutathione‐maleimide I, designated GS‐Mal. At 2 mM GS‐Mal reduces the rate of hexose uptake 80–100% in serum‐ and glucose‐starved CEF; in contrast A‐system amino acid uptake is unaffected. D‐glucose, but not L‐glucose or cytochalasin B, protects against GS‐Mal inhibition. These results are consistent with the hypothesis that sulfhydryl groups are involved in nutrient transport and that those sulfhydryls associated with the hexose transport system and essential for its function are located near the exofacial surface of the membrane in CEF.
The inhibitory effect of the artificial electron donor system, phenazine methosulfate‐ascorbate, on bacterial transport mechanisms
Authors: Eagon R. G. , Gitter B. D. , Rowe J. J. 
Published: May 2005

AbstractThe artificial electron donor system, phenazine methosulfate (PMS)‐ascorbate, inhibited active transort of solutes in Pseudomonas aeruginosa irrespective of whether the active transport systems were shock sensitive or shock resistant. N,N,N′,N′‐tetramethylphenylenediamine could be substituted for PMS but a higher concentration was required. PMS‐ascorbate also inhibited active transport in several other bacterial species with the exception of Escherichia coli and of a nonpigmented strain of Serratia marcescens. PMS‐ascorbate previously has been shown to energize active transport in isolated membrane vesicles, even those prepared from the same bacterial species in whose intact cells active transport was inhibited. The apparent Km of glucose active transport in untreated cells of P. aeruginosa was 40 μM while the Km of glucose transport in cells incubated with PMS‐ascorbate was 25 mM, and PMS‐ascorbate had no effect on efflux of accumulated glucose. These results strongly suggested that facilitated diffusion resulted upon exposure of the cells to PMS‐ascorbate. Thus, PMS‐ascorbate appeared to have an uncoupler‐like effect on cells of P. aeruginosa. The experimental data also pointed out that there are fundamental differences between the response of intact cells and membrane vesicles to exogenous electron donors.
Localization of some glycolipid glycosylating enzymes in the golgi apparatus of rat kidney
Authors: Fleischer Becca 
Published: May 2005

AbstractCell fractions from rat kidney were isolated and studied for their ability to synthesize several possible intermediates in the biosynthesis of sulfatides and gangliosides. The enzymes studied include UDP‐Gal:ceramide galactosyltransferase, UDP‐Gal:glucosylceramide galactosyltransferase, UDP‐Gal:galactosylceramide galactosyltransferase, and CMP‐NAN:lactosylceramide sialyltransferase activities. The initial glycosylation of ceramide was found to be present in all of the kidney cell fractions studied. The remaining glycosylating enzymes were largely localized in the Golgi apparatus of kidney. Thus, in addition to modifying glycoproteins for secretion, the Golgi apparatus in kidney is involved in the modification of a number of glycolipids which are destined to form cell membrane components.
Structural analysis of a membrane glycoprotein: Glycophorin A
Authors: Furthmayr Heinz 
Published: May 2005

AbstractGlycophorin A is the major sialoglycoprotein of the human erythrocyte membrane. Structural studies indicate that this molecule is made up of 3 domains composed of 2 hydrophilic segments which are separated by a region of 22 nonpolar amino acids. The N‐terminal half of the molecule contains all the carbohydrate associated with this protein.Glycophorin A forms high‐molecular‐weight complexes which can be dissociated only under certain conditions. The site of subunit interaction is located within the hydrophobic segment, which serves both to mediate protein‐protein and protein‐lipid interactions within the bilayer membrane. Glycophorin A spans the membrane presumably as a demeric complex with the carboxyterminal ends extending into the cytoplasm of the red cell. The transmembrane nature of the polypeptide chains finds strong support from the use of specific antibody‐ferritin conjugates applied to thin sections of fixed and frozen intact cells.Preliminary information on the analysis of human red cell variants which may lack some or all of the sialoglycopeptides are consistent with the presence in normal cells of a second sialoglycoprotein, provisionally labeled glycophorin B.
Prediction for secondary structures of ten proteins from the 50S subunit of the escherichia coli ribosome
Authors: Dzionara Michael , Robinson Stephen Michael Lewis , Wittmann‐Liebold Brigitte 
Published: May 2005

AbstractPredictions of the secondary structures of the following 10 proteins from the large subunit of the E. coli ribosome were made using their known amino acid sequences: L6, L16, L19, L27, L28, L30, L31, L32, L33, and L34. The predictions were made according to 4 different methods and the results for each protein are presented as diagrams indicating the conformational states, helix, extended structure, turn, and random coil, of each residue. From these diagrams, regions of highly probable secondary structure for the proteins are calculated. Estimates are made of the maximum possible lengths of the proteins in order to correlate these with the results obtained from antibody binding sites in the 50S subunit as determined by electron microscopy.