Double filament

Fig. 12. Polymorphism of filaments formed from the fusion protein constructs Ure2p1-65-GFP, Ure2p1 85-GFP, Ure2p1-90-GFP, and Ure2p1 95-GFP is illustrated with representative negatively stained micrographs of filaments. The panels are labeled (in white), according to the construct from which each filament was made. In projection, the filaments have a sinusoidal form whose wavelength is constant within a given filament but varies from filament to filament. The filament shown at top left is a double filament, consisting of two single filaments wrapped around each other. Bar = 200 nm.

The principal cytoskeletal proteins in non-muscle cells are actin, tubulin, and the components of intermediate filaments. Actin can exist either as monomers ( G-actin ) or polymerized into 70 A diameter double filament ( F-actin ). Polymerized actin usually is localized at the margins of the cells, linked by other proteins to the cell membrane. In contrast, tubulin forms hollow filaments, approximately 250 A in diameter, that are distributed within a cell in association, generally, with cell organelles. Stabilized microtubule structures are found in the flagella and cilia of eucaryotic cells however, in other instances - examples being the mitotic apparatus and the cytoskeletal elements arising in directed cell locomotion - the microtubules are temporal entities. Intermediate filaments, which are composed of keratin-like proteins, are approximately 100 A thick and form stable structural elements that impart rigidity, for example, to nerve axons and epithelial cells. 

Figure 2.26 a) Experimental arrangement of a single-filament thermal surface ionization source b) Schematic diagram of a double-filament arrangement for thermal surface ionization. (H. Kienitz (ed.), Massenspektrometric (1968), Verlag Chemie, Weinheim. Reproduced by permission of Wiley-VCH.)... 

Double Filament Evaporator 11 Ionizer Case Plate... 

Single, double and triple filaments have been broadly used in thermal ionization sources. In a single filament source, the evaporation and ionization process of the sample are carried out on the same filament surface. Using a double filament source, the sample is placed on one filament used for the evaporation while the second filament is left free for ionization. In this way, it is possible to set the sample evaporation rate and ionization temperature independently, thus separating the evaporation from the ionization process. This is interesting when the vapour pressure of the studied elements reaches high values before a suitable ionization temperature can be achieved. A triple filament source can be useful to obtain a direct comparison of two different samples under the same source conditions. 

The mass spectrometer we now use for zinc analysis, in the laboratory of Maynard Michel of Lawrence Berkeley Laboratory, is a thermal ionization mass spectrometer, a single direction focusing instrument with a 12" radius magnetic sector, double filament, rhenium ionizing source and electron multiplier detector. In addition, have done some preliminary work for Fe and Cu analysis with an automated TI/MS which speeds analysis considerably with excellent precision. We hope to be able to develop methods to use this automated Instrument for zinc analysis as well. 

Kober B. (1986) Whole-grain evaporation for Pb/ Pb-age-investigations on single zircons using a double-filament thermal ion source. Contrib. Mineral. Petrol. 93, 482-490. 

Infrared absorption spectra have been measured for NaF and KF isolated in solid argon. The fundamental modes of these species and the B3u, B2u, and Blu modes of (NaF)2 and (KF)2 are assigned assuming a planar rhomboid structure of D2h symmetry for the dimers.171 Surface ionization of lithium and its halides has been studied by a double-filament technique. At relatively high temperatures the temperature dependence of the lithium surface ionization current from all molecules studied was identical with that from lithium. Incomplete dissociation of LiCl can account for Li ionization threshold temperatures well above that for surface ionization of Li atoms. Dissociation energies of 4.8 0.1 eV for LiCl(g) and 4.3 0.1 eV for LiBr(g) were obtained.172 The equilibrium ionic forms in salt vapours have been studied. The concentration of M+ and X ions in the saturated vapours of MX (M = Na or K, X = halogen) at 850 °C is 107—1010 ions cm-3 and the concentration of M2X+ and M2X ions is 109—1011 ions cm-3, so that the vapours exhibit measurable electric conductivity. The equilibrium constants for the gaseous reactions are as follows ... 

Silk fibers, which are obtained from the secretion of the silkworm, are double filaments that are enclosed by a coating of a gum (sericin) as they are secreted. The amino acid sequence of the silk protein was shown to be (glycine-serine-glycine-alanine-glycine-alanine). The polypeptide chains are bound into antiparallel pleated )ff-sheet structures by hydrogen bonding. The structures are also held together by van der Waal forces. ... 

Figure 4.45 is an electron microphotograph of a dragline, showing that the dragline consists of a double filament even though it appears as a single filament... 

Fig. 4.45 Electron microphotograph of a dragline from a Nephila clavata spider. The dragline consists of double filaments, (a) side view, (b) cross section view.

Here, F is the force applied to the dragline, S is the cross sectional area of the double filament, L is the initial length of the dragline, and AL is the elongation of the dragline when the F is applied. The F and AL are determined from the force-elongation curve within the elastic limit point and the S from the electron scanning microscopy. 

Figure 7.1. Double-filament assembly thermal ionization source.

Fig. 15.4. From left (a) single filament, (b) double filament, and (c) triple filament assemblies for thermal ionization of metal salts and oxides. Reproduced from Ref. [3] with permission. John Wiley Sons Ltd, 1997.

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