Dimers, function

The oxygen affinity of the derivative was shown to be about half that of unmodified hemoglobin under similar conditions, but a degree of cooperativity was preserved. Kquilihrium and kinetic ligand-binding studies on this derivative have been interpreted (62) to show a perturbed R state. It is beheved that although the reaction is between the two P-chains, aP-dimers function independentiy, probably through a flexible connection. 

Milhgan, G. (2004) G protein-coupled receptor dimerization function and ligand pharmacology. Mol. Pharmacol. 66, 1-7. 

Such reactions may be of considerable significance. This is because, if two pendant p-coumarate linkages (or related molecules) are attached to two adjacent polysaccharide chains, an effective means of cross-linking via photochemical coupling could be achieved. However, there is no evidence at present to indicate that these dimers function as either intermolecular or intramolecular cross-linking reagents. 

FIGURE 19-11 Cytochrome be, complex (Complex III). The complex is a dimer of identical monomers, each with 11 different subunits. (a) Structure of a monomer. The functional core is three subunits cytochrome b (green) with its two hemes (bH and foL, light red) the Rieske iron-sulfur protein (purple) with its 2Fe-2S centers (yellow) and cytochrome ci (blue) with its heme (red) (PDB ID 1BGY). (b) The dimeric functional unit. Cytochrome c, and the Rieske iron-sulfur protein project from the P surface and can interact with cytochrome c (not part of the functional complex) in the intermembrane space. The complex has two distinct binding sites for ubiquinone, QN and QP, which correspond to the sites of inhibition by two drugs that block oxidative phosphorylation. Antimycin A, which blocks electron flow from heme bH to Q, binds at QN, close to heme bH on the N (matrix) side of the membrane. Myxothiazol, which prevents electron flow from... 

Chalcone and stilbene synthases are related plant PKSs [ 132]. Chalcones, such as naringenin chalcone, are produced as the biosynthetic precursors of flavinoids, while stilbenes are produced for their antifungal properties. Plant PKSs are likely to have evolved independendy from any of the aforementioned PKS and FAS systems [133, 134] and are atypical in many respects. These homodimeric enzymes consist of a single 40 kDa gene product (Fig. 2) [135]. The two active sites of the dimer function independently of one another [136]. Plant PKSs lack an AGP component, are not phosphopantetheinlyated, and act direcdy on CoA thioesters [134,137]. 

Ackers GK, Dalessio PM, Lew GH, Daugherty MA, Holt JM. Single residue modification of only one dimer within the hemoglobin tetramer reveals autonomous dimer function. Proc. Natl. Acad. Sci. USA 2002 99 9777-9782. 

Zhang J, Hosoya T, Maruyama A, Nishikawa K, Maher JM, Ohta T, Motohashi H, Fukamizu A, Shibahara S, Itoh K, Yamamoto M (2007b) Nrf2 Neh5 domain is differentially utilized in the transactivation of cytoprotective genes. Biochem J 404 459-466 Zhu M, Fahl WE (2001) Functional characterization of transcription regulators that interact with the electrophile response element. Biochem Biophys Res Commun 289 212-219 Zipper LM, Mulcahy RT (2002) The Keapl BTB/POZ dimerization function is required to sequester Nrf2 in cytoplasm. J Biol Chem 277 36544-36552... 

A. Sadlej, ]. Chem. Phys., 95, 6705 (1991). Exact Perturbation Treatment of the Basis Set Superposition Correction Based on the Constrained Dimer Function. 

Expanding the monomer and dimer functions into a basis set of atom-centered orbitals, 1. ) = V )> 4>n) = V )> the projections read ... 

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