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At least 19 recordsLinked to original sources
PubMed1991

Transitional elements with characteristics of both growth cones and presynaptic terminals observed in cell cultures of cerebellar neurons.

As growth cones interact with targets, they become presynaptic terminals by losing growth cone characteristics and acquiring presynaptic characteristics. Results presented here show that transitional elements can be identified in cell cultures of rat cerebellum, which have some characteristics of both growth cones and presynaptic terminals. During the first week in culture, slender growth cones have fine filopodia. Subsequently, many growth cones in contact with the polylysine substrate spontaneously enlarge and become non-motile. In transitional elements, the synaptic vesicle protein p65 extends into the peripheral domain and in some cases, extends into filopodia. Many of these transitional elements have active filopodia but show no movement over the substrate for periods of up to nine days. These transitional elements have lost the actin-rich peripheral domain of the growth cone but retain actin labelling in the filopodia. With electron microscopy, transitional elements were seen to contain accumulations of synaptic vesicles at the site of contact with the substrate. Electron microscopic immunocytochemistry showed these synaptic vesicles labelled for p65 with silver-developed gold particles. Thus, transitional elements have characteristics of both growth cones and presynaptic terminals, suggesting that they may also have functional attributes of both growth cones and presynaptic elements.

Actins↗
PubMed1975

Origin and early evolution of transition element enzymes.

In this paper we speculate on the origin and early evolution of transition element enzymes. Iron, molybdenum, and zinc, the most abundant transition elements in seawater, presumably complexed with compounds accumulated in the primeval sea in the course of chemical evolution forming compounds with subsequently evolved to form proenzymes or early enzymes with low activity and broad specificity. Iron complexes may be regarded as precursors of electron transfer enzymes, molybdenum complexes as precursors of enzymes involved in the metabolism of small molecules, and zinc complexes as precursors of hydrolytic and transferring enzymes, including enzymes participating in the metabolism of macromolecules and information transfer. The different iron, molybdenum, and zinc enzymes found in bacteria including Clostridium may then have arisen through specialization by increases in the enzyme specificity of these proenzymes. Copper would have been incorporated as an enzyme constituent after the elevation of environmental redox potential, probably due to the accumulation of atmospheric oxygen.

Aerobiosis↗
PubMed1988

Isolation of a vesicular intermediate in the cell-free transfer of membrane from transitional elements of the endoplasmic reticulum to Golgi apparatus cisternae of rat liver.

Preparations enriched in part-smooth (lacking ribosomes), part-rough (with ribosomes) transitional elements of the endoplasmic reticulum when incubated with ATP plus a cytosol fraction responded by the formation of blebbing profiles and approximately 60-nm vesicles. The 60-nm vesicles formed resembled closely transition vesicles in situ considered to function in the transfer of membrane materials between the endoplasmic reticulum and the Golgi apparatus. The transition elements following incubation with ATP and cytosol were resolved by preparative free-flow electrophoresis into fractions of differing electronegativity. The main fraction contained the larger vesicles of the transitional membrane elements, while a less electronegative minor shoulder fraction was enriched in the 60-nm vesicles. If the vesicles concentrated by preparative free-flow electrophoresis were from material previously radiolabeled with [3H]leucine and then added to Golgi apparatus immobilized to nitrocellulose, radioactivity was transferred to the Golgi apparatus membranes. The transfer was rapid (T1/2 of about 5 min), efficient (10-30% of the total radioactivity of the transition vesicle preparations was transferred to Golgi apparatus), and independent of added ATP but facilitated by cytosol. Transfer was specific and apparently unidirectional in that Golgi apparatus membranes were ineffective as donor membranes and endoplasmic reticulum vesicles were ineffective as recipient membranes. Using a heterologous system with transition vesicles from rat liver and Golgi apparatus isolated from guinea pig liver, coalescence of the small endoplasmic reticulum-derived vesicles with Golgi apparatus membranes was demonstrated using immunocytochemistry. Employed were polyclonal antibodies directed against the isolated rat transition vesicle preparations. When localized by immunogold procedures at the electron microscope level, regions of rat-derived vesicles were found fused with cisternae of guinea pig Golgi apparatus immobilized to nitrocellulose strips. Membrane transfer was demonstrated from experiments where transition vesicle membrane proteins were radioiodinated by the Bolton-Hunter procedure. Additionally, radiolabeled peptide bands not present initially in endoplasmic reticulum appeared following coalescence of the derived vesicles with Golgi apparatus. These bands, indicative of processing, required that both Golgi apparatus and transition vesicles be present and did not occur in incubated endoplasmic reticulum preparations or on nitrocellulose strips to which no Golgi apparatus were added.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1997

Binding of microtubules to transitional elements in oligodendrocytes of the myelin mutant taiep rat.

The presence of microtubules physically bound to smooth endoplasmic reticulum profiles of oligodendrocytes constitutes the most conspicuous feature observed in the myelin mutant taiep rat. The endoplasmic reticulum membranes associated with microtubules were morphologically characterized as transitional elements that constitute the intermediate compartment according to their topographic location close to the cis-Golgi apparatus. The development of this surprising microtubular defect appears to be associated with the early events of myelination. Transitional elements associated with microtubules operate in protein transport from endoplasmic reticulum to cis-Golgi. This microtubular defect could explain the dysmyelination and neurologic alterations observed in taiep rats. Moreover, these findings allow us to propose that there is a blockage of protein traffic at the intermediate compartment of taiep oligodendrocytes, a situation that could explain the hypomyelinated axons observed in this myelin mutant. The binding of microtubules to membranous organelles promotes the stabilization of microtubules, a feature that has important implications regarding its accumulation within the cytoplasm of oligodendrocytes during the temporal evolution of this neurologic disorder. The taiep rat is a myelin mutant with a long survival and could be a useful model for understanding dysmyelinating diseases in which the intracellular transport of myelin components is affected.

Animals↗
PubMed2003

Transition element contained partial-stabilized cement (PSC) as a dental retrograde-filling material.

A modified silicate cement has previously been developed as a dental retrograde filling; it has great sealing ability, good biocompatibility, and anti-bacterial properties. However, its clinical application is limited by a long setting time and poor handling property. In the present study, the setting time has been shortened by raising the preparation temperature of the cement and adding transition elements into the partial-stabilized cement (PSC) to increase the rate of hydration reaction of the cement. The rate of the hydration was evaluated by micro-hardness measurement. Phase transformation and micro-structure were examined by an X-ray diffractometer and a scanning electron microscope, respectively.When the preparation temperature increased (1400 degrees C), the phase content of Ca(2)SiO(5)(C(2)S) and Ca(3)SiO(6)(C(3)S) increased but the CaO decreased. The setting time was shortened and the micro-hardness increased because the increased amplitude of vibration of the atoms about their equilibrium resting positions increased by increasing the heating temperature. When the transition elements were added to PSC, crystal defects were effectively created and monoclinic structure of C(3)S was favored to form, which would increase the hydrated reaction of PSC and shorten the setting time. Co addition is the most effective due to its ability to create more defects and stabilize the monoclinic structure. The micro-hardness of the PSC with Co 5 wt% addition was about 66 in the Vickers scale. It also exhibited an early setting within 20 min. We believe that the modified PSC will have a great potential in its application to perforation repair and retrograde filling in endodontic surgery.

Dental Cements↗
PubMed2005

Databases for transition element bonding: metal-metal bond energies and bond lengths and their use to test hybrid, hybrid meta, and meta density functionals and generalized gradient approximations.

We propose a data set of bond lengths for 8 selected transition metal dimers (Ag(2), Cr(2), Cu(2), CuAg, Mo(2), Ni(2), V(2), and Zr(2)) and another data set containing their atomization energies and the atomization energy of ZrV, and we use these for testing density functional theory. The molecules chosen for the test sets were selected on the basis of the expected reliability of the data and their ability to constitute a diverse and representative set of transition element bond types while the data sets are kept small enough to allow for efficient testing of a large number of computational methods against a very reliable subset of experimental data. In this paper we test 42 different functionals: 2 local spin density approximation (LSDA) functionals, 12 generalized gradient approximation (GGA) methods, 13 hybrid GGAs, 7 meta GGA methods, and 8 hybrid meta GGAs. We find that GGA density functionals are more accurate for the atomization energies of pure transition metal systems than are their meta, hybrid, or hybrid meta analogues. We find that the errors for atomization energies and bond lengths are not as large if we limit ourselves to dimers with small amounts of multireference character. We also demonstrate the effects of increasing the fraction of Hartree-Fock exchange in multireference systems by computing the potential energy curve for Cr(2) and Mo(2) with several functionals. We also find that BLYP is the most accurate functional for bond energies and is reasonably accurate for bond lengths. The methods that work well for transition metal bonds are found to be quite different from those that work well for organic and other main group chemistry.

Journal Article↗
PubMed2002

Anomalous delay in wave propagation and tunneling: a transition-elements analysis of the traversal time.

An alternative model for near-field propagation and optical tunneling is proposed following the lines of the path-integral method developed by Feynman, and in particular by using a transition-elements analysis. Such a model was able to account for the frequency dependency of delay-time results of an experiment involving microwave propagation in the near field using two horn antennas [A. Ranfagni et al., Phys. Rev. E 66, 036111 (2002)]. Furthermore, this approach is also capable of interpreting delay-time results as a function of the barrier width in a frustrated total internal reflection experiment performed at the microwave scale and in the optical region.

Journal Article↗
PubMed2002

[Transitional elements and free radicals].

Iron and copper are essential trace elements, which in certain conditions, namely in the ionised form or in low-molecular complexes, can participate in single electron reactions and catalyse formation of free radicals, including the dangerous hydroxyl radical. Similar behavior have also some other transitive metals. Our overview is aimed on the role of transitive elements in the formation of free radicals and on the mechanisms that organisms have to prevent it. The highest attendance is given to the metabolism of iron and cooper. Consistent protection against free transitive metals (by binding with proteins, by oxidation or sequestration in a special compartment) enables organism to use their beneficial and required features without impairment of cell. Knowledge of these mechanisms provides the means to predict and effectively prevent the brake down of such defend systems in situations of the intravascular hemolysis, hemodialysis, administration of iron, impairments of the iron and copper metabolism, intoxication by oxidising substances etc.

Copper↗
PubMed1985

Squamous and transitional elements in rat bladder carcinomas induced by N-butyl-N-4-hydroxybutyl-nitrosamine (BBN). A study of cytokeratin expression.

Three hundred rat bladders bearing tumors induced by N-butyl-N-4-(OH)butyl-nitrosamine (BBN) were examined by routine histologic study and immunohistochemical staining of intermediate filament types. Smaller lesions were similar to human urothelial dysplasia histologically and immunohistochemically. Progression of the lesions demonstrated large exophytic papillomas with extensive endophytic epithelial growth into abundant stroma. These lesions showed increasing predominance of squamous over transitional elements. Immunohistochemical findings confirmed these results and also demonstrated that morphologically indifferent cells, even in early lesions, express heavier cytokeratins characteristic of keratinizing squamous epithelium. These results demonstrate that BBN-induced bladder tumors show marked quantitative and qualitative differences from the most common, purely transitional, human bladder carcinomas. However, the development in BBN-treated rat bladders of two tumor types, squamous and transitional, from an altered urothelium may serve as an attractive model for further study of the molecular genetics of keratin expression.

Animals↗
PubMed2000

A eukaryotic SWI2/SNF2 domain, an exquisite detector of double-stranded to single-stranded DNA transition elements.

Many members of the SWI2/SNF2 family of adenosine triphosphatases participate in the assembly/disassembly of multiprotein complexes involved in the DNA metabolic processes of transcription, recombination, repair, and chromatin remodeling. The DNA molecule serves as an essential effector or catalyst for most of the members of this particular class of proteins, and the structure of the DNA may be more important than the nucleotide sequence. Inspection of the DNA structure at sites where multiprotein complexes are assembled/disassembled for these various DNA metabolic processes reveals the presence of a common element: a double-stranded to single-stranded transition region. We now show that this DNA element is crucial for the ATP hydrolytic function of an SWI2/SNF2 family member: DNA-dependent ATPase A. We further demonstrate that a domain containing the seven helicase-related motifs that are common to the SWI2/SNF2 family of proteins mediates the interaction with the DNA, yielding specific DNA structural recognition. This study forms a primary step toward understanding the physico-biochemical nature of the interaction between a particular class of DNA-dependent ATPase and their DNA effectors. Furthermore, this study provides a foundation for development of mechanisms to specifically target this class of DNA-dependent ATPases.

Adenosine Triphosphatases↗
PubMed1979

Polymers produced by heating an amino acid mixture in sea water enriched with transition elements.

A mixture of eighteen protein amino acids was heated in sea water medium enriched with transition metal ions. Small granules were obtained as precipitates. Both dialyzable polymers and undialyzable polymers were obtained from the supernatant. Dialyzable polymers yielded mainly Glu, Asp, Ser, and Thr on hydrolysis; undialyzable polymers (C, 29.45; H, 3.87; N, 4.87; and ash, 31.5 wt%) yielded Thr, Asp, Glu, Gly, Leu, Ser, Lys, Pro, His, Phe, and a few unidentified ninhydrin positive peaks after acid hydrolysis. Five wt% of the undialyzable polymers con-ist of acid-hydrolyzable protein amino acids.

Amino Acids↗
PubMed2003

Molecular scale speciation of first-row transition elements bound to ligneous material by using X-ray absorption spectroscopy.

To develop a solid scientific basis for maintaining soil quality and formulating effective remediation strategies, it is critical to determine how environmentally-important trace metals are sequestered in soils at the molecular scale. The speciation of Mn, Fe and Cu in soil organic matter has been determined by synchrotron-based techniques: extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES). We show the structural similarity between the surface complexes of Mn(II), Fe(III) and Cu(II). These cations are bound to the surface through oxygen atoms. Each one presents a more or less tetragonal-distorted octahedral geometry. The use of X-ray absorption spectroscopy provides a relevant method for determining trace-metal speciation in both natural and contaminated environmental materials.

Journal Article↗
PubMed1976

[Interactions between various transition elements in their effect on pepsin activity].

Kinetic experiments were made with pepsin in the presence of Cu2+ ions and additional Fe2+, Ni2+ or Zn3+ ions as sulphates. As a parameter of the pepsin activity the turnover-rate curves were determined with haemoglobin as a substrate. An important activation of the pepsin was obtained by Cu2+ additions of 5-10(-4) mole/1. When Cu2+ and Fe2+ ions were added to the reaction mixture at the same time, an additive effect of both metal cations was observed. A competitive effect of both metal cations was found in the combination of Cu2+/Ni2+ ions. Zn2+ addition did not influence the activation of pepsin caused by Cu2+ ions.

Animals↗