Chemical cross-linking experiment

Chemical cross-linking experiments between rhodopsin and Gat indicate that residue 240 in IC 3 of rhodopsin is near the N- and C-termini of Ga, as well as the a4//J6 loop (Fig. 5 Cai et at., 2001 Itoh et at., 2001). Five residues at the C-terminus of Ga were shown to specifically interact with four noncontiguous residues in IC 3 (Liu et at., 1995). Peptides corresponding to IC 3 also cross-link to the N-terminus of Ga and the C-terminus of G/J (Taylor et at., 1994, 1996). As mentioned previously, the binding site for the C-terminal peptide of Gat was mapped to the inner face of helix VI (Janz and Farrens, 2004), and both the Ga and Gy C-termini of Gt interact with IC 4 of rhodopsin (Ernst et at., 2000). These data provide important information about specific contacts between receptors and G proteins however, more constraints are needed to improve our current model of the receptor-G protein interface. 

The schematic drawing of the structure and the function of sMMO is shown in Scheme 1. sMMOs, which are composed of three components as described above, function upon complexation of these components. Therefore, it is important to know how these three components are bound to each other. The studies for clarifying the architecture of the enzyme complex of sMMO from M. trichosporium OB3b were carried out by chemical cross-linking experiments using l-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) [50]. Such a study indicates that protein B is bound to an a-subunit of MMOH and the reductase is bound to p-subunit of MMOH. In addition to these... 

An important question concerning ligand binding valency centers on the oligomeric state of the CI-MPR. It is clear that the receptor does not exist as a disulfide-bonded higher order complex and, when solubilized in detergent, the receptor is a monomer [9]. However, chemical cross-linking experiments [23] and gel filtration studies performed in the presence of a bound lysosomal enzyme [9] indicate a dimeric subunit composition. Thus, the receptor either ... 

Re A5. The experiment shows that no chain disentangling takes place after introduction of chemical cross-links in the strained state. Chain disentangling may take place prior to cross-linking if the relaxation period is long enough. 

Other experiments with Cys mutants and fluorescence labels and chemical cross-linking on Sup35pNM filaments (Krishnan and Lindquist, 2005) support the view that the regions from residues 21 to 38 and from 86 to 106 may also have a parallel in-register arrangement. 

The most important distinction between the two structures is that only the helical model is compatible with all of the published structural data, including results obtained from limited proteolysis [81,83], chemical cross-linking [83], analytical ultracentrifugation [81], and mutant complementation [84,85]. Although the double helix provides a useful model with good predictive power, it will no doubt be subjected to further investigation by, for example, atomic force microscopy or X-ray crystallography. Such experiments should refine the structural information on PKSs, and point the way toward the productive modification and immobilization of the synthases. 

Conventionally, cross-link density is determined by measurements of the modulus, the glass transition temperature T, and by solvent uptake in swelling experiments. In these procedures, the chemical cross-link density cannot be discriminated from network-... 

Preparation of chemically cross-linked fibers Chemical cross-linking was achieved by extrusion of solutions of E- and K- pairs of polymers at equal concentrations of functional groups into a saturated solution at 50 C of water soluble carbodiimide (EDC, l-(3-dimethy-laminopropyl)-3-ethylcarbodiimide) to form amide bonds between the carboxyl of glutamic acid (E) residues and the e-amino groups of lysine (K) residues. When in an adequately hydrophobic elastic protein-based polymer, the charged carboxylate and amino functions experience a driving force for ion-pairing. The force... 

Nawawi and Hassan (2003) prepared homogeneous (unmodified) and cross-linked chitosan (extracted from shrimp shells) membranes. Chitosan membranes were modified via a chemical cross-linking technique. PV experiments were done using an IPA-water system. From the PV experiments, it was observed that chitosan membranes exhibited preferential permeation to water. The modified chitosan membrane showed a lower permeation flux, but a higher separation factor than the unmodified membranes. The modified chitosan membrane had a better PV performance than the unmodified membranes in terms of a PSI. 

Characterization of Poiymer Networks by Transverse Relaxation. The NMR transverse magnetisation relaxation experiments were extensively used for quantitative analysis of the density of chemical cross-links, temporary and trapped chain entanglements and physical network junctions which are formed in fllled rubbers, semicrystalline and ionic containing elastomers, and for determination of the molecular-scale heterogeneity of polymer networks ((83), and reference therein). 

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