Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “self-assembly”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed1984

[Changes in the ratio of microsomal electron carriers in reconstituted microsomal membranes].

The reconstitution of microsomal membrane monooxygenase system with variable contents of the hydroxylating chain enzymatic components was carried out. It was found that during self-assembly of microsomal membranes solubilized with 4% sodium cholate and gel filtration through Sephadex LH-20 in the presence of isolated microsomal enzymes, two forms of cytochrome P-450, i. e. phenobarbital- and 3-methylcholantrene-induced ones, and NADPH-cytochrome P-450 reductase, the exogenous enzymes are incorporated into the microsomal membrane matrices of control and methyl-cholantrene-treated animals. In the membranes reconstituted from the microsomes of the methylcholantrene-induced animals the catalytic activity of cytochrome P-448 in the metabolism of benz(a)pyrene at varying cytochrome P-448 and NADPH-cytochrome P-450 reductase contents were investigated.

Animals↗
PubMed1984

[Catalytic activity of cytochrome P-448 in native and reconstituted microsomal membranes].

The dependence of oxidative activity of a microsomal monooxygenase system on the ratio of its constituent enzymes--cytochrome P-448 and NADPH-cytochrome P-450 reductase--was investigated. Two approaches for preparation of microsomal membranes with different contents of cytochrome P-448 were used, i. e., time-dependent induction by 3-methylcholanthrene and reconstitution of microsomal membranes by self-assembly from a mixture of solubilized microsomes of intact and methylcholanthrene-induced rats. Using antibodies against cytochrome P-448, the cytochrome P-448 content in native and reconstituted microsomal membranes and its participation in hydroxylation of benz(a)pyrene was determined. It was shown that benz(a)pyrene is hydroxylated in a membrane microsomal monooxygenase system more effectively, when the ratio of NADPH-cytochrome P-450 reductase to cytochrome P-448 is 1: 3 to 1: 6.

Animals↗
PubMed1984

Cholesteric organization of DNA in vivo and in vitro.

In concentrated solutions DNA organizes spontaneously to form the "cholesteric" phase which is one type of liquid crystal. We have reproducibly obtained both continuous cholesteric phases and isolated cholesteric globules in equilibrium with the isotropic phase. A comparison is made between this in vitro cholesteric organization and dinoflagellate chromosomes which present the same organization in vivo. The observed defects are analyzed in the two cases. It appears that the cholesteric organization is due to self-assembly phenomena and that the shape of globules and chromosomes is due both to surface tensions and to the presence of defects.

Chromosomes↗
PubMed1982

Construction of bacterial flagellar filaments, and aspects of their conversion to different helical forms.

The helical flagellar filaments of bacteria such as Salmonella typhimurium are constructed from subunits of a single protein called flagellin by a process of self-assembly. They are polymorphic, and change from one helical form to another in a variety of circumstances. This paper discusses, from a viewpoint of classical mechanics, two types of problem associated with these filaments. First is the general problem of how to construct a helical rod from identical subunits. There must be some variation in the pattern of packing of subunits; and it is demonstrated that a mechanically bi-stable but otherwise linear-elastic subunit can build filaments which are not only helical but also possess the observed polymorphic properties. The question of uniqueness of the design is discussed. The second problem concerns the hydrodynamic performance of a helical filament which can switch waveform when subjected to mechanical overload. Transitions which can be brought about in this way are reviewed briefly. An explanation is offered in terms of the mechanics of polymorphism for the behaviour of an anomalous and puzzling 'partly rotating' filament in Hotani's (1979) micro-video study of tethered filaments in fluid streams.

Bacteria↗
PubMed1980

[Structural organization of membranes reconstituted from phospholipids and subchromatophore pigment-protein complexes].

Pigment--protein complexes of the P870 reaction centers and complexes of the bacteriochlorophyll light-harvesting antenna were isolated from the chromatophores of the non-sulfur purple bacterium Rhodospirillum rubrum by solubilization with detergents. The proteoliposomes containing the reaction centers or reaction centers and the light-harvesting antenna as well as liposomes formed from phospholipids were obtained by a self-assembly procedure using seya bean phospholipids. The freeze-fracture study showed that the proteoliposomes contain a large amount of globular particles. The particles incorporated into the two types of the proteoliposomes were distinguished in size. The globules of the reaction center and antenna complexes were bigger in size than the reaction center globules. The globular structures were not found in the liposomal membranes. The liposomes formed in the absence of the pigment--protein complexes were predominantly the multilamellar vesicles. The proteoliposomes were mostly represented as monolamellar membrane vesicles. The spatial arrangement of the reaction center complexes in the membranes is discussed.

Bacterial Chromatophores↗
PubMed1983

[Reconstitution of membranous microsomal monooxygenase system during gel filtration on Sephadex LH-20].

Solubilization of liver microsomes of intact, phenobarbital-treated and 3-methylcholantrene-treated rats was investigated. It was shown that treatment of microsomes with 4% sodium cholate leads to separation of proteins and phospholipids from the microsomal membrane. The microsomal solubilizate was passed through lipophilic Sephadex LH-20 and the particles whose properties are close to those of the microsomal ones were obtained. The high efficiency of self-assembly of the microsome-like particles, e. g. lack of cytochrome P-450 conversion into cytochrome P-420, high microsomal protein yield and the high level of metabolizing activity of microsomal monooxygenase, was demonstrated.

Animals↗
PubMed1983

Assembly of unfertilized sea urchin egg tubulin at physiological temperatures.

Tubulin was purified from unfertilized eggs of the sea urchin Strongylocentrotus purpuratus by DEAE-column chromatography and cycles of temperature-dependent assembly and disassembly. Tubulin-containing column fractions self-assemble into intact microtubules in the absence of high molecular weight microtubule-associated proteins. Egg microtubules assembled during the third cycle of assembly following DEAE-chromatography are composed of 2 or 3 alpha tubulins and 2 beta tubulins as assayed by isoelectric focusing and two-dimensional electrophoresis. The critical protein concentrations necessary for assembly of egg tubulin at 37 and 25 degrees C are 0.15-0.24 and 0.24-0.28 mg/ml, respectively. At physiological temperatures, the critical protein concentrations are 0.81 mg/ml at 15 degrees C and 0.70-0.79 mg/ml at 18 degrees C. At 18 degrees C, bovine brain microtubule-associated proteins stoichiometrically stimulate the initial rate and final extent of egg tubulin assembly. These hybrid microtubules assemble at 18 degrees C at a critical protein concentration of 4-20 micrograms/ml.

Animals↗
PubMed1983

Time-lapse microcinematographic and phase contrast studies on the cell reformation of Chirocephalus yolk granules in vitro.

In this article we report on a time-lapse microcinematographic and phase contrast study of the cell reformation of yolk granules which were isolated from mature oocytes in the genital sac of the middle female intersex of Chirocephalus nankinensis. The observations on yolk granules were made in fixed positions and the morphological changes of cell reformation were continuously recorded in vitro. The transformation of yolk granules into cellular structures may be tentatively described as follows: At the early stages in culture, it can be seen that the granular or bubbly structures gradually appear within the hyaloid and homogeneous yolk granules; the appearance of yolk granules gradually changes from elliptical into round shape. With further transformation, their appearances in general take the shape of oblate spheroids, their size is smaller than before and inside the yolk granules their granular and bubbly structures become more and more obvious. Finally, the nuclear and cellular structures can be seen in these transforming yolks. By means of time-lapse microcinematographic and phase contrast examinations in fixed positions, single yolk granules obtained from the mature oocyte with little amounts of adhering cytoplasm are continuously recorded and have been shown to occur, steadily and gradually build up cellular structures by self-organization and self-assembly. Up to the present, we have cultured these kinds of cellular organizations repeatedly. Therefore, it can be concluded that the existence of cell reformation on the basis of yolk granules according to the dynamic morphological changes is an objective reality.

Animals↗
PubMed1983

[Analysis of the stability of the intermediate fibrin polymers formed in a fibrinogen-thrombin system].

Intermediate fibrin polymers formed from fibrinogen at low thrombin concentrations under physiological conditions are studied for their stability. Smith's statement that intermediate fibrin oligomers are inert molecules whose further self-assembly is possible only under additional thrombin activation was not supported. It is shown that the intermediate fibrin polymer stability at pH 7.4 is not high because of a strong tendency to aggregation and the higher molecular weight of the polymer the less its stability. The polymer stability in solution increases with pH. Stability of soluble fibrin complexes in solution depends on their size, defined by environmental conditions and on the quantity of fibrinogen present.

Animals↗
PubMed1980

Dynamics of linear protein polymer disassembly.

This report presents a kinetic model for endwise depolymerization of linear, self-assembling protein systems. We develop a reliable method for predicting the shape of depolymerization curves (remaining polymer weight versus time) on the basis of the initial polymer length distribution. Computer simulations are used to illustrate changes in the polymer length distribution and average polymer weight during disassembly. In addition, our method provides an accurate determination of the microscopic rate constant for subunit release. Application of this analysis to dilution-induced and cold induced disassembly of microtubules is illustrated in the preceding paper (Karr, T.L., Kristofferson, D., and Purich, D.L. (1980) J. Biol. Chem. 255, 8560-8566). A survey of other possible applications of this treatment to microtubules, flagella, F-actin, and tobacco mosaic virus protein is included.

Actins↗
PubMed1978

Monoclonal IgG anticoagulants delaying fibrin aggregation in two patients with systemic lupus erythematosus (SLE).

There is paucity of information regarding the prolonged plasma thrombin time known to occur in some patients with systemic lupus erythematosus. Detailed investigations of plasma from two such patients disclosed that IgG accounted for this defect in each case. IgG isolated from plasma of either patient possessed the property of delaying fibrin aggregation and prolonging the clotting times of fibrinogen. Preincubation of IgG from either patient with anti-IgG or anti-Fab (rabbit) serum abolished this anticoagulant property. Moreover, the anticoagulant IgG from the first patient was neutralized with anit-k chain and anti-IgG3, that from the second patient with anti-lambda chain and anti-IgG1 serum. These anticoagulants were also dissimilar with respect to their interactions with fibrin(ogen). IgG from the first patient had no anticoagulant activity against fibrin(ogen) species lacking intact Aalpha chains. IgG from the second patient displayed undiminished anticoagulant effect on such fibrin(ogen) species. We conclude that each anticoagulant interacted with a distinct region(s) on the fibrinogen molecule and that these interactions affect or involve sites that participate in the fibrin self-assembly process.

Adolescent↗
PubMed1980

Structural studies of the assembly of simple viruses.

The principles of structural design and the bonding properties of structural proteins form a basis for the study of virus assembly. Virus coat proteins are designed specifically to interact with one another and with the viral nucleic acid to form a stable virus particle. The process of assembly is controlled by the switching of protein subunit conformation, which can alter the binding properties of the subunits. The self-assembly processes of several simple viruses in vitro have significantly different rates of assembly and specificities for their viral nucleic acid. It is possible that many viruses have multiple pathways for assembly, each pathway exhibiting somewhat different characteristics but all resulting in identical infectious virus particles.

Bacteriophages↗
PubMed1982

Tubulin polymerization in dimethyl sulfoxide.

The self-assembly of tubulin devoid of microtubule-associated proteins (MAPs) has been studied using a MES buffer containing dimethyl sulfoxide (Me2SO). Between 6% and 12% v/v Me2SO, the tubulin forms polymers which resemble microtubules in their morphology and chemical properties. These Me2SO microtubules, like normal microtubules, require GTP for assembly and are sensitive to cold, calcium ions, colchicine, and hydrostatic pressure. The polymerization shows a critical concentration which is dependent on the concentration of Me2SO. 8% Me2SO was found to be the optimum concentration for microtubule assembly. In these conditions, a linear Van t'Hoff plot is obtained, with delta H0/kJ . mol-1 = 26.5 over the range of 10-35 degrees C, and delta S0/J . K-1 . mol-1 = 186, in contrast to the assembly with MAPS or glycerol. The kinetics of polymerization shows that the apparent stoichiometry coefficient of nucleation has the value of 2. Ultracentrifugation analysis shows that there are no oligomers present at low temperatures in the absence of free nucleotide, while in identical conditions, tubulin with MAPs does form oligomers. Although the solvent conditions used supported propagation of assembly, nucleation was found to be very dependent on the transiently locally high Me2SO concentrations formed when Me2SO was added to initiate assembly. It is concluded that Me2SO preferentially stabilizes the lateral interactions.

Animals↗
PubMedDate not supplied

[Molecular arrangement of protochlorophyll aggregated forms in solid films].

The conditions were found for the successive self-assembly of two protochlorophyll aggregated forms in solid films with absorption maxima at 647 (+/-1) nm (PChl 647) and 651 (+/-1) nm (PChl 651) and fluorescence maxima at 653-655 nm and 654-657 nm, respectively. These forms model the native photochemically active form of the precursor of chlorophyll (chlorophyllide) in plants (P650). The investigation of infrared spectra (in the region 1800-1600 cm-1), CD-spectra and fluorescence, carried out in this study, permitted in between the indicated forms to distinguish the type of the molecular arrangement of aggregated structures, PChl 647 is supposed to consist of unstable dimers formed without the participation of keto groups of the cyclopentanone rings, while the structure of PChl 651 includes the dimers to bind more firmly by the intermolecular bonds formed at the expense of keto groups and a central magnesium atom.

Chlorophyll↗
PubMed1981

[Properties of reconstituted transhydrogenase from mitochondria].

The membrane vesicles (proteoliposomes) have been reconstituted from soya bean phospholipids and mitochondrial transhydrogenase (EC 1.6.1.1) by a self-assembly procedure. Palmitoyl-CoA and Mg2+ inhibit the rate of NAD+ reduction by NADPH in these proteoliposomes as well as in these submitochondrial particles. After solubilization of transhydrogenase from submitochondrial particles membranes the specific activity of the enzyme decrease and then again increases (more than 4.5 times) after its incorporation into the proteoliposomal membranes. An addition of potassium cholate to the proteoliposomal suspension further increases the rate of the direct transhydrogenase reaction (by 35--40%) due to the function of the oppositely oriented molecules of transhydrogenase. The Michaelis constants for NAD+ and NADPH for transhydrogenase proteoliposomes are 27 microM and 30 microM, respectively. These data are practically coincident with the results obtained for submitochondrial particles (21 and 33 microM, respectively). Thus, the incorporation of transhydrogenase into proteoliposomal membranes results in reconstitution of both electrogenic and the most essential kinetic properties of the enzyme.

Animals↗
PubMedDate not supplied

[Study of aggregation of chlorophyll and its analogs in artificial pigment--protein complexes].

Investigations of synthetic pigment-protein complexes by the spectral methods showed that during chlorophyll complex formation with casein self-assembly of different pigment packing that are analogous to the system of their native forms according to spectral properties, takes place. Under the condition of the links between protein and methylchlorophyllide, the latter has slighter and pheophytin has greater tendency to aggregation that chlorophyll. The conclusions are based on our results and data on the nature of chlorophyll-protein interaction and structure of spectral forms of pigment. Monomers are fixed on the protein by the coordination of Mg atoms. Oligomers are fixed electrostatically by polar sides of porphyrin cycles free of pigment-pigment interaction. Dimers and chlorophyll-water aggregates are fixed hydrophobically by phytol residuals.

Caseins↗
PubMed1976

Biogenesis of matrix vesicles in cartilage growth plates.

Although the structure and function of cartilage matrix vesicles have been comprehensively documented in the literature, the method of vesicle production and export to the extra-cellular matrix is less well understood. The existing data are grouped into four general hypotheses of matrix vesicle biogenesis, with a consideration of the relative merits and weaknesses of each postulate. The hypotheses are: a) budding from cellular processes; b) extrusion of preformed structures; c) cellular degeneration and disintegration; and c)subunit secretion and extracellular assembly. Each of these possibilities offers conceptual advantages and disadvantages, so that it is difficult to adopt a monistic stance. Previous notions of vesicle biogenesis have derived from statis morphologic and analytical data, which are necessarily limiting when attempting to draw kinetic conclusions. Radiotracer studies of lipid synthesis and transport in cartilage lead to the conclusion that matrix vesicles in the growth plate are derived from chondrocytes; the present data favor the hypotheses of budding from cellular processes and/or subunit secretion with extracellular self-assembly.

Cartilage↗
PubMed1977

Myogenesis and contraction in the early embryonic heart of the rainbow trout. An electron microscopic study.

Myogenesis in the embryonic heart of the rainbow trout, Salmo gairdneri (Rich.), was investigated electron microscopically from the 29th to the 41st somite stage. Thick and thin myofilaments are formed simultaneously as well as precursors of Z-lines, to which the thin filaments are attached. The genesis of filaments takes place in the region around the intracellular yolk droplets. The first myofibrils appear by the 33rd somite stage, probably formed by a mechanism of self-assembly in which the binding sites of actin and myosin participate. A- and I-bands do not develop before the 38th osmite stage. The contraction already begins during the 33rd somite stage in the middle of the tubular heart. Gradually, the peristaltic waves spread increasingly to other parts of the heart. In the 41st somite stage the entire heart is contractile and all myocytes contain myofibrils.

Animals↗