Pentameric structure

Caenorhabditis elegans is a soil nematode that has been subjected to detailed genetic analysis. The possible structure of the nematode levamisole receptor, based on the pentameric structure of the nicotinic channel of the Torpedo electric organ (Devillers-Thiery et al, 1993), is shown in Fig. 21.12. 

The palladium-catalyzed formation of sulfides can generate polyphenylene sulfide from a dithiol and a dibromoarene, or from 4-bromobenzenethiol (Equation (38)).17 In 1984 Asahi Glass obtained patents for the formation of this polymer in the presence of palladium and nickel catalysts.125,126 In addition, Gingras reported palladium-catalyzed couplings of aryl halides and thiols to form discrete phenylene sulfide oligomers.127,128 A number of polyphenylene sulfide wires, ranging from dimeric to pentameric structures, were prepared by the palladium coupling, albeit in modest yields ... 

IgM 1-2 (5-10%) Pentameric structure secreted from B cells during primary response potent binder of complement high levels indicative of systemic lupus erythematosus or rheumatoid arthritis cannot cross placenta... 

The ionotropic receptors have a pentameric structure. The most important of these, the NMDA receptors, are assembled from two... 

The results of this study indicated that chloroplast-synthesized CTB-2L21 protein displays a strong affinity for GMl gangliosides in a similar manner to that found for purified bacterial CTB. This indicates that the fusion protein retained the correct pentameric structure characteristic of CTB and... 

GABA and glycine. Glycine receptors are pentameric structures that are selectively permeable to . Strychnine, which is a potent spinal cord convulsant and has been used in some rat poisons, selectively blocks glycine receptors. 

The GABAa receptor has a pentameric structure assembled from five subunits (each with four membrane-spanning... 

This picture was made by mathematically filtering electron micrographs of ordered, two-dimensional arrays of the receptor. Each of the four pentameric structures shown represents an individual acetylcholine receptor with its central transmembrane pore. The dark areas indicate the five subunits (a2fiy8). (From R. M. Stroud, M. P. McCarthy, and M. Schuster, Nicotinic acetylcholine receptor superfamily of ligand-gated ion channels,... 

FIGURE 22.1 Pentameric structure of IgM IgM is composed of a pentamer of the basic four chain structure held together by inter H chain disulfide bonds. The heavy chain (p) has four constant domains. A small, cysteine rich protein called J chain initiates cross linking of C3 and C4 of five IgM monomers to make the circulating, pentameric form of IgM. 

Fig. 6b.—A view of an ATOMS diagram of the part of the X-ray crystal structure of methyl 4,6-0-benzylidene-2,3-0-dibutylstannylene-a-D-mannopyranoside (21a) that contains the first three monomeric units of the pentameric structure.55 The first monomeric unit is on the right. Tin atoms are solid black circles, oxygen atoms are unfilled circles, carbon atoms are intermediate with those in the butyl groups being lighter.

The five-membered methylarsenic ring has been characterized by various methods. A single-crystal X-ray study has shown that the solid consists of discrete cyclic pentamers with equal As-As distances. The ring is puckered with mean As—As—As bond angles of 102°. Methyl groups are arranged in such a way that a staggered conformation at the As—As bonds results. Electron diffraction measurements of the vapour of the yellow form are consistent with the cyclic pentameric structure. ... 

The B subunits of CT and LT (CTB and LTB, respectively) form a homo-pentameric structure that is critical for toxin-cell interaction, whereas the A subunits of both CT and LT (CTA and LTA, respectively), after cleavage near their carboxy termini with trypsin or similar proteases, followed by reduction of a single disulfide bond, yield the enzymatically active Ai peptide and a smaller A2 peptide (Spangler,... 

The next increase in aggregation state of Group 11 (IB) metal thiolates affords pentameric structures, but to the best of our knowledge a structurally characterized species of this type is unknown. In organocopper(I) chemistry, the only example is that of mesitylcopper [Cu5(C6H2Me3-2,4,6)5] (125), which has a structure based on an open Cu5C5 10-membered heterocycle. 

Avian IgM is closely related to mammalian IgM. It cross-reacts strongly with human IgM (Mehta et al., 1972), also has a pentameric structure (Feinstein and Munn, 1969) and its J-chain cross-reacts with human J-chain (Kobayashi et al., 1973). Purified preparations of IgM often contain IgY due to the tendency of the latter to aggregate. 

The pentameric structure of the GABAa receptor has binding sites for benzodiazepines (BZ receptors) and for other drugs, including barbiturates and ethanol. 

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