bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hexagonal packing of lipid acyl chains and membrane plasticity
Authors: Dorset D. L. , Hui S. W. , Strozewski C. M. 
Published: May 2005

AbstractElectron microscope and electron diffraction observations on microcrystals of pure lipids (a phosphatidylethanolamine, two phosphatidylcholines, a phosphatidic acid, and a galactocerebroside) reveal an extreme flexibility of lipid layers when the acyl chains are hexagonally packed (d100 = 4.17 Å). This is corroborated by similar observations on wet bilayers of a lecithin. It is shown that more “crystalline” polymethylene packings do not impart such plasticity to lipid layers and are therefore an unsuitable structural matrix for dynamic biological membranes.
Trapping at low temperature of oriented chloroplasts: Application to the study of antenna pigments and of the trap of photosystem‐1
Authors: Vermeglio A. , Breton J. , Mathis P. 
Published: May 2005

AbstractA technique is described for the preparation of oriented samples from spinach chloroplasts whose linear dichroism is then studied by (flash) absorption spectroscopy. The chloroplasts are suspended in a glycerol‐containing medium, oriented in a magnetic field, and slowly cooled in the magnet until the medium is rigid enough to avoid disorientation effects.The absorption spectra in polarized light have been measured at −50° and −170°C. They allow the orientation of chlorophyll b to be resolved, and the red transition moment is found to be tilted out of the membrane plane.A study of the flash‐induced absorption changes linked to Photosystem‐1 activity reveals a progressive evolution of the difference spectra and of the linear dichroism with decreasing temperatures. At −170°C, the difference spectrum of P700 in the red is well resolved. All transition moments are found to be largely parallel to the membrane plane.The potential use of the technique for other experiments by differential absorption spectroscopy and by EPR techniques is discussed.
Cytoskeletal elements of chick embryo fibroblasts revealed by detergent extraction
Authors: Brown Susan , Levinson Warren , Spudich James A. 
Published: May 2005

AbstractTreatment of chick embryo fibroblasts with 0.5% Triton® X‐100 extracts most of the cell protein, leaving an organized part of the cell structure attached to the tissue culture dish. This “Triton cytoskeleton” consists largely of intermediate‐sized filaments and bundles of microfilaments. SDS polyacrylamide gel electrophoresis reveals that this cytoskeleton is made up of three main proteins. One protein component is 42,000 daltons and co‐migrates with muscle actin. The other two components are 52,000 and 230,000 daltons and remain quantitatively associated with the cytoskeleton during the detergent extraction. The possible identity of these three protein components and their organization into a supramolecular structure is discussed.
Localization and organization of microfilaments and related proteins in normal and virus‐transformed cells
Authors: Goldman Robert D. , Yerna Marie‐Jeanne , Schloss Jeffery A. 
Published: May 2005

AbstractThe localization and organization of actin‐like microfilaments in normal, SV‐40 and adenovirus transformed cells are determined by the coordinated use of light optical, electron optical and biochemical techniques. In adenovirus‐type 5 transformed hamster embryo cells, microfilament meshworks appear to be the predominant organizational form of cellular actin, while in normal hamster cells, microfilament bundles are prevalent. Differences between 3T3 and SV‐40 transformed 3T3 cells are less apparent and may be related to the packing and intracellular distribution of microfilament bundles. Attempts at relating these ultrastructural changes in transformed cells to the images obtained following reaction with fluorescein‐labelled myosin fragments and indirect immunofluorescence with smooth muscle myosin antibody are discussed. In several instances the fluorescence microscope images do not correspond to the ultrastructural observations. The results are discussed in terms of the possible relationships between alterations in cytoplasmic contractile elements and the abnormal behavior of transformed cells.
Fine structural localization of concanavalin a binding sites on hamster spermatozoa
Authors: Kinsey William H. , Koehler James K. 
Published: May 2005

AbstractThe plasma membrane of epididymal spermatozoa of the golden hamster (Mesocricetus auratus) exhibits morphological differences over various parts of the head and tail as detected by air‐dried replicas and freeze‐etching techniques. In an attempt to ascertain whether any topographical differences exist in the number or distribution of carbohydrate moieties associated with the cell surface, cells were labeled with Concanavalin A and marked with hemocyanin.It was found that while the plasma membrane over the acrosomal region differed from that of the postacrosomal region in membrane components revealed by freeze fracturing, there was no apparent difference in the distribution or density of Con A binding sites detectable by hemocyanin localization. The tail regions exhibited differences in both fracture face appearance and the distribution of detectable carbohydrate moieties.It was also found that binding sites for Concanavalin A exist on the inner and outer acrosomal membranes in addition to those on the plasma membrane.
Microtubles and actin filaments in teleost visual cone elongation and contraction
Authors: Burnside Beth 
Published: May 2005

AbstractTeleost retinal cones contract in light and elongate in darkness. This paper describes the disposition of microtubules and cytoplasmic filaments in cone cells of 2 species of fish (Haemulon sciurus and Lutjanus griseus). In Haemulon, the neck‐like “myoid” region of the cone changes in length from 5 μ to 75 μ. Maximal observed rates of elongation and contraction are comparable to that of chromosome movement in mitosis (2–3 μ/min). Microtubules presumably participate in cone elongation, since numerous longitudinal microtubules are present in the myoid region, and colchicine blocks dark‐induced elongation.Myoid shortening, on the other hand, appears to be an active contractile process. Disruption of microtubules in dark‐adapted cones does not produce myoid shortening in the absence of light, and light‐induced myoid shortening is blocked by cytochalasin‐B. Cone cells possess longitudinally‐oriented thin filaments which bind myosin subfragment‐1 to form arrowhead complexes typical of muscle actin. Myoid thin filaments are clearly observed in negatively stained preparations of isolated cones which have been disrupted with detergent after attachment to grids. These myoid filaments are not, however, generally preserved by conventional fixation, though bundles of thin filaments are preserved in other regions of the cell. Thus, actin filaments are poorly retained by fixation in precisely the region of the cone cell where contraction occurs. Cone cells also possess longitudinally‐oriented thick filaments 130–160Å in diameter. That these thick filaments may be myosin is suggested by the presence of side‐arms with approximately 150 Å periodicity. The linear organization of the contractile apparatus of the retinal cone cell makes this cell a promising model for morphological characterization of the disposition of actin and myosin filaments during contraction in a nonmuscle cell.
Cytoskeletal functions of cytoplasmic contractile proteins
Authors: Pollard Thomas D. 
Published: May 2005

AbstractThis is a review of the evidence that the cytoplasmic contractile proteins function as a cytoskeletal system inthe cytoplasmic matrix. Biochemical experiments show that cycoplasmic actin filaments can form a solid gel under conditions likely to exist in living cells. The actin filaments are associated with other proteins which may stabilize the gel and which are involved with motile force generation like myosin. Ultrastructural studies show that actin filaments are difficult to preserve, but that under stabilizing conditions networks of actin filaments are found throughout the cytoplasmic matrix.
Genetic control of membrane mosaicism
Authors: Satir Birgit 
Published: May 2005

AbstractThe mosaic and dynamic character of cellular membranes is illustrated by the specific intramembrane particle array, the fusion rosette, found to be essential for memberane fusion and secretion in the ciliated protozoa, Tetrahymena and Paramecium. The rosette is not a permanent site within the membrane. When secretion of mucocysts is synchronized by treating cells with the local anesthetic dibucaine, all rosettes disappear, only to reassemble as new mucocysts mature. Assembly of the functional rosette is under genetic control. A series of secretory mutants of Paramecium, blocked in various stages of the secretory cycle, has been studied (11). Mutants that do not secrete lack the fusion rosette, although other intramembrane particle components of the fusion site are present. Certain properties of the rosett, in particular its particle partition coefficient, are temperature‐dependent, which may affect the ability of the rosette particles to assemble. A temperature‐sensitive mutant, nd9, secretes normally, and has rosettes at 18°C, but fails to secrete attached trichocysts at 27°C.
Comparison of the structural and chemical composition of giant T‐even phage heads
Authors: Aebi U. , Bijlenga R. K. L. , ten Heggeler B. , Kistler J. , Steven A. C. , Smith P. R. 
Published: May 2005

AbstractA study has been made of the structure of the capsids of T4D giant phage produced from mutants in gene 23 and temperature‐sensitive mutants in gene 24, and T4D and T2L giant phage formed by the addition of L‐canavanine followed by an L‐arginine chase in the growth medium.All the giant phage capsids have been shown to be built according to the same geometrical architecture. This consists of a near‐hexsagonal surface net, lattice constant 129.5 Å, folded into a left‐hand T = 13 prolate icosahedron elongated along one of its fivefold symmetry axes. Their only apparent difference from wild‐type T‐even phage capsids is their abnormally elongated tubular part.A comparison of the capsomere morphologies and protein compositions of the giant phage capsids showed that all T4D giants are indentical but differ from T2L: The T4D capsomere has a complex (6+6+1)‐type morphology, whereas the T2L has a simple 6‐type. T2L phage, however, lack two capsid proteins, “soc” and “hoc”, present in T4D. The difference in capsomere morphology can therefore be related to the difference in the protein compositions of these two phage.Possible differences between the initiation and means of length regulation of giant phage heads and the aberrant polyheads are discussed.
Involvement of microtubules and microfilalments in the action of vasopressin in canine renal medulla
Authors: Iyengar Ravi , Lepper Kenneth G. , Mailman David S. 
Published: May 2005

AbstractVasopressin‐stimulated cyclic AMP content and the uptake of 3H2O and 22Na into canine renal medullary slices were measured. Cyclic AMP was increased threefold by 9 × 10−9M vasopressin in isotonic (290 mOsm/kg H2O) Krebs‐Ringers bicarbonate. A significant increase in vasopressin‐stimulated 3H2O uptake began at 2.75 min after hormone addition and lasted until 5.00 min. Colchicine (1 × 10−5 M) inhibited the vasopressin‐ stimulated 3H2O uptake. This effect required a minimum preincubation period of 30–40 min in colchicine‐containing medium. Colchicine had no effect on basal or vasopressin‐stimulated cyclic AMP (10 mM). Lumicolchicine (10−5M) had no effect on either vasopression‐ or dibutyryl cyclic AMP‐stimulated 3H2O uptake. 14 C‐colchicine bound predominantly to the cytosol fraction enriched in microtubules, while virtually no binding was observed on plasma membranes. Loght‐microscopic examinations of cross sections of tissue slices showed that a majority of vasopressin‐treated collecting tybulels and some control tubules had occluded lumens. Colchicine‐treated cells, in the presence of vasopressin, had open lumens indicating a blockage of the vasopressin‐induced water transport. Cells treated with cytochalasin B (1 μgm/ml) also had open lumens in the presence of vasopressin. Cytochalasin B also blocked vasopressin and dibutyryl cyclic AMP‐stimulated 3H2O uptake into collecting duct cells but had no effect on vasopressin stimulated cyclic AMP levels. It was concluded that microtubules and possibley microfilaments are involved in the subcellular mechanism by which vasopresssin increases the permeability of the collecting duct to water.
Intracellular regulation of cell shape and motility in naegleria. First insights and a working hypothesis
Authors: Fulton Chandler 
Published: May 2005

AbstractAmoebae of Naegleria gruberi differentiate to temporary flagellates that have a regular, asymmetric, streamlined body contour. During the hour‐long differentiation, amoeboid movement gradually ceases and as a consequence the cells round up. Subsequent elongation to flagellate shape includes the formation of a microtubular cytoskeleton. Both the loss of amoeboid motility and the formation of the flagellate shape require prior transcription and translation, suggesting the possibility that specific syntheses of RNA and protein may be required for each shape change. Flagellates can “revert” to motile amoebae within 20 sec after a suitable stimulus, indicating that the amoeboid motility system remains latent in flagellates. A cell‐produced chemical factor extracted from Naegleria, Ψ, triggers a reproducible sequence of rapid shape changes in flagellates when added to their environment. Cells respond to the presence of external Ψ only “transiently,” and the reaction of flagellates to added Ψ requires extracellular Ca+2. Ionophore A23187 produces shape changes in flagellates similar to those produced by Ψ, supporting the conclusion that Ψ is involved in the movement of Ca+2. Normally Ψ is intracellular, and the intracellular distribution of Ψ changes during differentiation.These results lead to and support a working hypothesis to explain the rapid changes in shape and motility in Naegleria. Four elements are postulated: Ca+2; an actin‐based amoeboid motility system that depends on free Ca+2 for functioning; a tubulin‐based cytoskeleton that assembles and remains assembled only when free Ca+2 is low; and Ψ. The factor Ψ is postulated to regulate the intracellular release of Ca+2. According to the hypothesis, intracellular free Ca+2 is constantly swept up into Ca‐reservoirs. Motility of amoebae depends on local release of Ca+2 from these reservoirs, which in turn is caused by the intracellular release of Ψ. During differentiation, Ψ is “compartmentalized” as part of the developmental program, and as a consequence intracellular Ca+2 is swept up into Ca‐reservoirs but not released. As free Ca+2 becomes limiting, amoeboid movement stops, and the cells round up. Subsequently, in a process that depends on low free Ca+2, the microtubular cytoskeleton is assembled, and the flagellate shape is formed. During reversion of flagellates to amoebae, release of Ψ from its “compartments” permits local release of Ca+2, which then causes both disassembly of the flagellate cytoskeleton and immediate resumption of amoeboid movement. This testable hypothesis has implications for the study of cell shape, motility, and differentiation.
Isolation of the alanine carrier from the membranes of a thermophilic bacterium and its reconstitution into vesicles capable of transport
Authors: Hirata Hajime , Sone Nobuhito , Yoshida Masasuke , Kagawa Yasuo 
Published: May 2005

AbstractA carrier protein mediatine alanine transport was purified from the membranes of the thermophilic bacterium PS3, by ion exchange chromatography in the presence of both Triton X‐100 and urea.The alanine carrier was recovered in the nonadsorbed fraction from either DEAE‐or CM‐cellulose columns, suggesting that its isoelectric point was in the neutral pH region.The final preparation contained virtually no electron transfer components, ATPase, or NADH dehydrogenase. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed that the final preparation consisted of two major protein components with molecular weights of 36,000 and 9,400.Active transport of alanine after incorporation of the alanine carrier into reconstituted proteoliposomes was driven not only by an artificial membrane potential generated by potassium ion diffusion via valinomycin but also by mitochondrial cytochrome oxidase incorporated into the same liposomes and supplemented with both cytochrome c and ascorbic acid.The membrane‐integrated portion (TF0) of the ATPase complex uncoupled alanine transport by conducting protons across the membrane.
Role of the membrane potential in serum‐stimulated uptake of amino acid in a diploid human fibroblast
Authors: Villereal Mitchel L. , Cook John S. 
Published: May 2005

AbstractThe Na+‐dependent accumulation of α‐aminoisobutyric acid (AIB), measured in normal growing and quiescent (serum‐deprived) HSWP cells (human diploid fibroblast), was found to be twofold higher (AIBin/AIBout = 20–25) under the normal growing conditions. Serum stimulation of quiescent cells increases their AIB concentrating capacity by approximately 70% within 1 hr. These observations suggest that the driving forces for AIB accumulation may be reversibly influenced by the serum concentration of the growth medium. Addition of valinomycin (Val) to cells preequilibrated with AIB causes an enhanced accumulation of AIB, suggesting that the membrane potential can serve as a driving force for AIB accumulation. After preequilibration with AIB in 6 mM K+, transfer to 94 mM K+ with Val results in a marked and rapid net loss of AIB. The effect of Val on the accumulation of AIB is greatest in quiescent cells, with the intracellular AIB concentrations reaching those seen both in Val‐stimulated normal cells and in Val‐stimulated serum‐stimulated cells. By adjusting [K+]0, in the presence of Val, the membrane potential of growing cells can be matched to that of quiescent cells or vice versa. When this is done, the two accumulate AIB to the same extent. Hence the AIB accumulating capacity is characteristic of the membrane potential rather than of the growth state. In summary, these data suggest that the accumulation of AIB in HSWP cells is influenced by changes in membrane potential and that a serum‐associated membrane hyperpolarization could be responsible for the increased capacity for AIB accumulation in serumstimulated cells.
Hormonal regulation of hepatic amino acid transport
Authors: Kilberg Michael S. , Neuhaus Otto W. 
Published: May 2005

AbstractThe transport of 2‐aminoisobutyric acid (AIB) into liver tissue was increased by both insulin and glucagon. We have now shown that these hormones do not stimulate the same transport system. Glucagon, possibly via cAMP, increased the hepatic uptake of AIB by a mechanism which resembled system A. This glucagon‐sensitive system could be monitored by the use of the model amino acid MeAIB. In contrast, the insulin‐stimulated system exhibited little or no affinity for MeAIB and will be referred to as system B. On the basis of other reports that the hepatic transport of AIB is almost entirely Na+ dependent and the present finding that the uptake of 2‐aminobicyclo [2,2,1] heptane‐2‐carboxylic acid (BCH) was not stimulated by either hormone, we conclude that system B is Na+ dependent. Furthermore, insulin added to the perfusate of livers from glucagon‐pretreated donors suppressed the increase in AIB or MeAIB uptake. Depending upon the specificities of systems A and B, both of which are unknown for liver tissue, the insulin/glucagon ratio may alter the composition of the intracellular pool of amino acids.
Distribution of a major surface‐associated glycoprotein, fibronectin, in cultures of adherent cells
Authors: Mosher Deane F. , Saksela Olli , Keski‐Oja Jorma , Vaheri Antti 
Published: May 2005

AbstractFibronectin was present in media and cell layers of cultures of adherent cells from human skin, kidney, lung, chest wall, liver, and heart. Cell‐surface fibronectin, visualized by immunofluorescence, was in dense fibrillar (cultures from lung), discrete fibrillar (e.g., cultures from skin), or punctate (some cultures from kidney) structures. The subunit sizes of cell‐surface fibronectin and fibronectin soluble in medium appeared identical in sodium dodecyl sulfate‐polyacrylamide gels. To explain the polymorphism of cell‐surface fibronectin, there must be chemical differences among the fibronectins synthesized by different cell strains or factors in the cell layer which influence fibronectin binding and aggregation.
Properties of a penicillium GDP‐mannose: Glycopeptide mannosyltransferase solubilized with triton X‐100
Authors: Gander J. E. , Fang Faye 
Published: May 2005

AbstractMembranes from Penicillium charlesii were separated into 6 fractions by sucrose density gradient ultracentrifugation. The least dense fraction (ρ = 1.1 g cm−3) contained GDP‐mannose: glycopeptide mannosyltransferases that transferred [14C] mannose onto mannopyranosyl‐(seryl/threoyl)‐polypeptide and phosphogalactomannan regions of peptidophosphogalactomannan. Approximately 90% of the [14C] mannose incorporated was isolated as mannobiose following treatment of peptidophosphogalactomannan with 0.5 N NaOH. The remainder was located in phosphogalactomannan. About 10% of the membrane‐bound mannosyltransferase activity was solubilized with 1% Triton X‐100. The soluble mannosyltransferase activity was purified by affinity chromatography on peptidophosphogalactomannan‐Sepharose 4B and ammonium sulfate fractionation. Mannose incorporation was shown to be a function of the concentration of added acceptor. No incorporation occurred in the absence of added acceptor or when MgCl2 was substituted for MnCl2. Peptidophosphogalactomannan, phosphogalactomannan, phosphomannan, and mannan, each obtained by appropriate treatment of peptidophosphogalactomannan from P. charlesii, served as mannosyl acceptors. In contrast, α‐mannosidase treated peptidophosphogalactomannan did not serve an acceptor of mannosyl residues. Up to 70% of the mannose from GDP‐mannose was transferred to added acceptor. Treatment of [14C] mannosyl‐labeled peptidophosphogalactomannan with 0.5 N NaOH released 90% of the [14C] mannose as phosphogalactomannan and the remainder was released as mannobiose. [14C] Mannose‐labeled phosphogalactomannan was subjected to acetolysis. Mannobiose was the major [14C]‐labeled product isolated. Significant quantities of [14C] mannose were isolated also. These results show that soluble mannosyltransferase catalyzes the formation of (1–6)‐linked mannosyl residues as well as the transfer of a mannosyl residue to a (1–6)‐linked mannosyl residue in the phosphogalactomannan. The specificity of the enzyme is shown by its inability to catalyze mannosyl transfer to α‐mannosidase treated peptidophosphogalactomannan, or to incorporate more than 2 mannosyl residues onto the phosphogalactomannan region. Presumably the second mannosyl residue is attached by a (1–2) linkage as the mannan contains only (1–6)‐ and (1–2)‐linked mannosyl residues (Gander et al: J Biol Chem 249:2063, 1974). No evidence was obtained for the participation of a lipid‐linked mannosyl‐containing intermediate in this system.