Terminal complexes labeling

Terminally deuterium-labeled phenylacetylene was also used to elucidate the possible mechanism of this reaction. In view of all these results, a rationalization for the loss of the trimethylsilyl and the migration of the ethoxy group from its original position in the complex 96 has been put forward. Due to the contribution of the conjugated diarylcyclopentadiene moiety in 98 and 99, these molecules showed intense fluorescence with a relatively high quantum yield of 46%. 

Figure 4 Ribbon diagrams of glycosyltransferases that demonstrate the different structural folds. When possible, nucleotide-donor sugars are depicted as stick models, manganese is depicted by a magenta ball, and N- and C-terminals are labeled. GT-A fold members are represented by bovine pi,4-galactosyltransferase I complexed with UDP-Gal (5) (Fig. (4)a, PDB accession number 1O0R) and by human polypeptide...

IMMUNOGOLD LABELING OF CELLULOSE-SYNTHESIZING TERMINAL COMPLEXES... 

It is well known that the rosette and linear terminal complexes (TCs) can be observed by the freeze-fracture replication technique. The structures revealed by this technique are known as putative cellulose-synthesizing TCs. Kimura et al. (1999) demonstrated that TCs in vascular plants contain cellulose synthases using a novel technique of sodium dodecyl sulfate (SDS)-solubilized freeze fracture replica labeling (SDS-FRL). The localization of the cellulose synthase to the TC was accomplished almost 40 years after the hypothesis of Roelofsen (1958) in which he stated that enzyme complexes could be involved in cellulose biosynthesis. It has been more than 30 years since the discovery of the first TC by Brown, Jr. and Montezinos (1976) and in particular, 26 years after the discovery of rosette TCs in plants by Mueller and Brown, Jr. (1980). 

Figure 14-2. Comparison of SDS-FRL and conventional freeze-fracture techniques (a) freeze fracturing, (b) shadowing, (c) chromic acid treatment, (c ) Cellulase and SDS treatment, (d) antibody labeling. (Figure 2 from Itoh, T. and Kimura S. 2001. Cellulose synthases are localized in terminal complexes. Journal of Plant Research 114 483-489. Reproduced with kind permission of Springer Science and Business Media and the Botanical Society of Japan).

The novel highly substituted spiro[4.4]nonatrienes 98 and 99 are produced by a [3+2+2+2] cocyclization with participation of three alkyne molecules and the (2 -dimethylamino-2 -trimethylsilyl)ethenylcarbene complex 96 (Scheme 20). This transformation is the first one ever observed involving threefold insertion of an alkyne and was first reported in 1999 by de Meijere et al. [81]. The structure of the product was eventually determined by X-ray crystal structure analysis of the quaternary ammonium iodide prepared from the regioisomer 98 (Ar=Ph) with methyl iodide. Interestingly, these formal [3+2+2+2] cycloaddition products are formed only from terminal arylacetylenes. In a control experiment with the complex 96 13C-labeled at the carbene carbon, the 13C label was found only at the spiro carbon atom of the products 98 and 99 [42]. 

The dominant factors reversing the conventional ds-hydroboration to the trans-hydroboration are the use of alkyne in excess of catecholborane or pinacolborane and the presence of more than 1 equiv. of EtsN. The P-hydrogen in the ris-product unexpectedly does not derive from the borane reagents because a deuterium label at the terminal carbon selectively migrates to the P-carbon (Scheme 1-5). A vinylidene complex (17) [45] generated by the oxidative addition of the terminal C-H bond to the catalyst is proposed as a key intermediate of the formal trans-hydroboration. 

The structure of the major aggregate was identified by labeling studies. Since the major set has two equal intensity 6Li signals, these signals could be assigned as a 1 1 complex 68 of lithium acetylide and lithium alkoxide or a dimer (such as 69) of the 1 1 complex 68 shown in Figure 1.9. Both structures have two different Li species. In order to discriminate between 68 and 69, a terminal acetylene carbon of 37 was labeled with 13C. In the case of 68, both lithium signals will be a doublet... 

FIGURE 1.10 Various possible surface species on a Pt or Pd (111) surface. A and B represent possible locations of 1,2-di-a-Cj 2-cyclohexane, and C, D, and E represent possible locations of Jt-complexed Jt-C -cyclohexene. Full complements of hydrogens are assumed at each angle and terminal that is not either a- or Jt-bonded to a surface site as indicated by a small circle. Half-hydrogenated states, which are mono-a-C -adsorbed species (where n is the number of the carbon attached to the surface), would be represented by one small circle at the carbon bonded to a surface site. F, G, and I represent possible locations of Jt-C -cyclohexene. F shows the three carbons of the Jt-allyl moiety adsorbed in three adjacent three-point hollow sites and G shows it over one three-point hollow site, whereas I shows adsorption over the approximate tops of three adjacent atoms. (Note Label H is not used to avoid confusion with hydrogen, which is not shown.)... 

The solution structures of Raf-, Rif-, and RalGDS-RBD were solved and, in addition, NMR spectroscopy was used to probe the interaction with Ras [211, 213,219]. Only the RBD was labeled with 15N and the shifting of distinct cross peaks (HSQC spectra) due to binding of Ras allowed one to identify the binding surface on the RBD. Consistent with X-ray structures of the complexes (see above) in both Raf and RalGDS, amino acid residues located in (31 and (32 and the C-terminal part of al are involved in the interaction with Ras. 

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