No abstract available

[en] The small GTPase Rab7 controls fusion and transport of late endocytic compartments. A critical mediator is the Rab7 effector RILP that recruits the minus-end dynein-dynactin motor complex to these compartments. We identified a natural occurring splice variant of RILP (RILPsv) lacking only 27 amino acids encoded by exon VII. Both variants bind Rab7, prolong its GTP-bound state, and induce clustering of late endocytic compartments. However, RILPsv does not recruit the dynein-dynactin complex, implicating exon VII in motor recruitment. Clustering might still occur via dimerization, since both RILP and RILPsv are able to form hetero- and homo-dimers. Moreover, both effectors compete for Rab7 binding but with different outcome for dynein-dynactin recruitment and transport. Hence, RILPsv provides an extra dimension to the control of vesicle fusion and transport by the small GTPase Rab7

No abstract available

[en] The dimerisation of 3,4-dimethoxy-12-benzyloxy stilbene 1 with 15 equivalent of ferric chloride (FeCl₃) 60% w/v for 12 hours afforded unnatural products, a pallidol-like compound 2 and an ampelopsin F analogue, 3 (molecular formula 2, 3 = C₄₆H₄₂O₆). By using High Resolution-Electron Impact Mass Spectrometer (HR-EIMS) technique, we found that the mass spectrum of 2 showed significant mass peaks. This allows us to suggest several fragmentations, compatible to the peaks. The mass spectrum of 2 exhibited molecular ion peak as 713.2869, compatible with the presence of pallidol analogue (690) associated with sodium adduct (23). The loss of methyl group gave single oxygen which presumed unstable, followed by deformation with new bonding with proton thus giving m/z 676. M/z 508 was resulted from the loss of benzyl oxybenzene. The base peak was indicated by the m/z 294, where bis cyclopentane transformed to cyclo octa-1,5-diene having two aromatic rings attached with methoxy and single oxygen. The presence of 1 during fragmentation was remarked as the fragment molecular formula compatible with m/z 242. Meanwhile, the protonated molecular ion peak of 3 was observed to give compatible molecular formula 690. The fragmentation of 3 exhibited the occurrence of highly stabilized tropylium cation (C₇H₇⁺). The loss of benzyl oxybenzene and benzyloxy led to fragment having m/z 417. It was followed by the cleavage of the benzyloxy to present fragment with m/z 401. We concluded that the spectra were more informative than those published from previous study. (author)

[en] Receptor activator of nuclear factor κB-ligand (RANKL) transduces a differentiation signal appropriate to osteoclasts likely through induction a receptor homotrimer; however, biological importance of RANK-trimerizarion is unknown. To address the signaling mechanism of the RANK receptor, we analyzed the effect of two different types of homodimer inducers RANK-TM-FKBP36v and hEpoR-RANK-TM on osteoclastogenesis. Dimerizing component FKBP36v or extracellular portion of human erythropoietin receptor (hEpoR) was fused to RANK lacking the extracellular domain, and the dimerization of this fusion protein was induced by addition of the chemical inducer of dimerization AP20187 or erythropoietin, respectively. Such treatment resulted in induction of TRAP-activity, a marker of osteoclast in a dose dependent manner, with an efficiency equivalent to that of induction by RANKL. However, dimerized-RANK-induced osteoclasts showed relatively low levels of multinucleation, pit forming activity, and expression of calcitonin receptor and cathepsin K, compared with osteoclasts which were induced in the presence of RANKL. As expression of nuclear factor of activated T cells 1 (NFATc1) was also reduced in dimerized-RANK-induced osteoclasts, RANK oligomerization by RANKL is a critical event to generate fully matured osteoclasts through upregulation of NFATc1

[en] Studying the activity of any catalyst and selectivity toward special products is easy by selecting a module reaction, and choosing appropriatecondition. In our case the reaction of α- methylstyrene dimerization was a choice to study the activity of mordenite type zeolite crystallized from natural clay mineral (kaolin P-2), and also the selectivity toward dimers.The prepared catalyst in the form of hydrogen showed that the acceptable activity and selectivity to linear dimers were (72.5%), at 80 °C, and atmospheric pressure. Different products from the dimerization of α- methylstyrene over prepared catalyst was investigated, and the conversion rate reached to 73%wt. (paper)

[en] A tendency to dimerize in the presence of lipids was found for the protegrin. The dimer formation by the protegrin-1 (PG-1) is the first step for further oligomeric membrane pore formation. Generally there are two distinct model of PG-1 dimerization in either a parallel or antiparallel β-sheet. But despite the wealth of data available today, protegrin dimer structure and pore formation is still not completely understood. In order to investigate a more detailed dimerization process of PG-1 and if it will be the same for another type of protegrins, in this work we used a high-resolution NMR spectroscopy for structure determination of protegrin-3 (RGGGL-CYCRR-RFCVC-VGR) in the presence of perdeuterated DPC micelles and demonstrate that PG-3 forms an antiparallel NCCN dimer with a possible association of these dimers. This structural study complements previously published solution, solid state and computational studies of PG-1 in various environments and validate the potential of mean force simulations of PG-1 dimers and association of dimers to form octameric or decameric β-barrels

[en] Highlights: All 18 [4+2] channels of pyridine dimerization were fully studied. Involvement of N atom in DA reaction causes high barrier height, otherwise the barrier heights are low. The regularity obtained in this study is also meaningful for predicting further polymerization of pyridine. Compared to [4+2] covalent dimerization of benzene, [4+2] covalent dimerization of pyridine is more easier. The Diels-Alder (DA) covalent dimerization mechanisms of pyridine were studied at the MP2/6-311G(d,p) level. Involvement of N atom in DA reaction causes high barrier height, otherwise the barrier heights are low. The two most stable D_I dimers formed by intermolecular DA reaction (^b-γD_I and ^b-γ⿲D_I) and the two most stable D_II dimers formed by further intramolecular DA reaction (^c-γD_II and ^c-γ⿲D_II) were located with relative energy of 26.6 and 26.1 kcal/mol, and 32.1 and 31.6 kcal/mol, respectively, higher than two moles of pyridines. Theoretical results suggested that DA dimerization of pyridine is slightly easier than that of benzene.

[en] The metal concentration and matrix conditions which favor the dimerization of vanadium atoms to divanadium molecules are quantitatively assessed using optical spectroscopy. A simple kinetic theory is presented which enables small metal clusters to be identified in the presence of atomic species. This approach makes use of the fact that a metal atom being deposited is capable of diffusing either on the matrix surface or within a narrow region (the reaction zone) near the matrix surface before its kinetic energy is dissipated sufficiently to immobilize it. The surface diffusion pathway is found to predominate over the statistical generation of dimers. The kinetic result, which suggests that V₂ is formed on the matrix surface rather than in the gas phase, is also borne out by the intriguing observation that for a given metal deposition rate the dimer-to-monomer ratio decreases as one increases the atomic weight of the noble gas used to isolate them, with Ar giving the most V₂ and Xe the least. Careful concentration experiments in Ar, Kr, and Xe matrices permit the uv--visible transitions of V₂ to be identified and the extinction coefficient ratio epsilon/sub V//epsilon/sub V/2 to be determined. A qualitative molecular orbital description of V₂ is presented in the light of iterative extended Hueckel calculations. These computations suggest that high spin divanadium has a strong metal--metal bond which is mainly 4s in character with only small contributions from the degenerate d/sub x z, y z/ π-bonding set. Visible absorptions observed in the 600--450 nm region are tentatively assigned to electronic transitions localized mainly between the V--V sigma-bond and the d-orbital manifold

[en] (−)-Epigallocatechin gallate (EGCG), which is the most abundant bitter polyphenol in green tea (Camellia sinensis) leaves, is generally unstable under oxidative conditions. In this study, the efficient dimerization of EGCG was successfully achieved without changes in stereochemistry by treatment with nonthermal dielectric barrier discharge (DBD) plasma. The stereochemically pure dimers 2 and 3 connected by a methylene linkage exhibited significantly enhanced melanogenesis inhibitory activities compared to the parent EGCG and the active compounds 2 and 3 suppressed cellular tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2 expression in B16F10 melanoma cells, which could be considered one of the mechanisms of action. These results indicate a new method for efficient dimerization of stereochemically active depigment agent induced by DBD plasma treatment. (paper)