SI fragment

Figure 14.15 Stmcture of the SI fragment of chicken myosin as a Richardson diagram (a) and a space-filling model (b). The two light chains are shown in magenta and yellow. The heavy chain is colored according to three proteolytic fragments produced by trypsin a 25-kDa N-terminal domain (green) a central 50-kDa fragment (red) divided by a cleft into a 50K upper and a 50K lower domain and a 20-kDa C-terminal domain (blue) that links the myosin head to the coiled-coil tail. The 50-kDa and 20-kDa domains both bind actin, while the 25-kDa domain binds ATP. [(b) Courtesy of 1. Rayment.]...

The third approach (path c) requires that a chain containing at least two carbon atoms be present in AN. As a mle, AN can be smoothly transformed into ene nitroso acetals B, which (like standard enamines) can react with electrophiles to give the target nitronates through elimination of the Si+ fragment (for more details, see Section 3.5.4). 

Figure 4.5. Structure of myosin. Myosin comprises both light and heavy chains. The heavy chains may be cleaved by trypsin to generate light meromyosin (LMM) and heavy mero-myosin (HMM). Papain digestion of HMM yields subfragments SI and S2 each SI fragment contains an ATPase site and an actin-binding site. The light chains modify the activity of the ATPase.

Using film an,d delay-line detectors on the DESY and XI1 benches, a study of the binding of exogeneous myosin heads (SI fragments) to insect fli t muscle in the rigor... 

The charge is primarily retained by the Si fragment, and Ei produces a less intense peak. 

TABLE 21. Geometric parameters in compounds containing the Si-S- -Si fragment... 

FIGURE 19. Histogram of Si—S bond lengths in compounds containing Si—S—Si fragments... 

The first mercury(I) silyl complex [(Me3SiMe2Si)3Si]2Hg2 was prepared by the reaction of an excess of (Me3SiMe2Si)3SiH with (t-Bu)2Hg. The solid structure of the complex displays linear Si—Hg—Hg—Si fragment with regular metal-silicon bond lengths... 

In this arrangement the typical easy-to-analyse INADEQUATE appearance is lost. The 2D plot would contain 29Si double-quantum frequencies (i.e. sum of the chemical shifts of the two coupled silicon nuclei) along axis FI and XH frequencies along the F2 axis. A pair of cross-peaks at the same 29Si double-quantum frequency would indicate a Si—Si fragment two cross-peaks with the same XH frequency indicate a Si—Si H fragment. 

FIGURE 54. 29Si NMR spectra (IGD) of the 3-deuterio derivative 39 under conditions of proton noise decoupling (a) and with selective proton decoupling of (CH3)3Si protons (b). The line due to silicon from the 2HC(3)—O—Si fragment is the line that does not exhibit any splitting in spectmm b. Reproduced by permission of John Wiley Sons, Ltd from Reference 167... 

The silicon atom in 1-bromo-p-trimethylsilylpentaborane (Table 9) is penta-coor-dinated. Structural parameters, however, point to a tetrahedral configuration of the fragment (Si(CH3)j, i.e., to sp hybridization of Si atom. The B -Si fragment can be described in terms of three-center two-electron bonds involving quasitetrahedral silicon orbitals and orbitals of each boron atom... 

Figure 34.3. Myosin Dissection. Treatment of muscle myosin with proteases forms stable fragments, including subfragments SI and S2 and light meromyosin. Each SI fragment includes the head (shown in yellow and pink) from the heavy chain and one copy of each light chain (shown in blue and orange).

Figure 34.4. Myosin Structure at High Resolution. The structure of the SI fragment from muscle myosin reveals the presence of a P-loop NTPase domain (shaded in purple). An a helix that extends from this domain is the binding site for the two light chains.

Figure 34.10. Lever-Arm Motion. Two forms of the SI fragment of scallop muscle myosin. Dramatic conformational changes are observed when the identity of the bound nucleotide changes from ADP-V043- to ADP or vice versa, including a nearly 90-degree reorientation of the lever arm.

Multiple field data can be used to determine the dominant interaction and to provide an estimate of the quadrupole interaction even when a distinct quadrupole lineshape cannot be discerned. As an example, the linewidths of the Ti-O-Si fragments in the above amorphous gel determined at 5.6 and 14.1 T are shown in Table 6.1. 

Let us first consider the structure of myosin. The results of electron microscopic studies of skeletal-muscle myosin show it to be a two-headed structure linked to a long stalk (Figure 34.2). As we saw in Chapter 33, limited proteolysis can be a powerful tool in probing the activity of large proteins. The treatment of myosin with trypsin and papain results in the formation of four fragments two SI fragments an S2 fragment, also called heavy... 

A carbon analogue of 44, containing an ether moiety C-O-C instead of the Si-O-Si fragment, appears not to have been described in the literature but should be a stable compound. However, its preparation is expected to be more difficult than that of the disiloxane 44, the synthesis92 of which is straightforward. 

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