Protein binding of coherin and other small molecules by thin-layer gel chromatography

The protein binding stoichiometry of small molecules is here determined on a nanomole scale by a simplified procedure utilizing chromatography on thin layers of cross-linked dextran gels. New data are presented on the thin layer chromatographic properties of representative ligands, including a-amino acids, peptides, dyes and fluorigenic reagents, in relation to their molecular weights, polar characteristics, gel water regain values and denaturants, providing criteria for the general application of this method to studies of ligand binding with large as well as small molecules. By this procedure coherin peptides, A1 and B1--4, respectively, bind to coherin C in the molar ratio, 2:1, with a binding constant of about 10(5) M-1. Coherin C is believed to act as a carrier peptide.     

Variable-temperature, variable-field magnetic circular dichroism studies of tris-hydroxy- and mu3-oxo-bridged trinuclear Cu(II) complexes: evaluation of proposed structures of the native intermediate of the multicopper oxidases

Multicopper oxidases catalyze the 4e- reduction of O2 to H2O. Reaction of the fully reduced enzyme with O2 produces the native intermediate (NI) that consists of four oxidized Cu centers, three of which form a trinuclear cluster site, all bridged by the product of full O2 reduction. The most characteristic feature of NI is the intense magnetic circular dichroism pseudo-A feature (a pair of temperature-dependent C-terms with opposite signs) associated with O --> Cu(II) ligand-to-metal charge transfer (LMCT) that derives from the strong Cu-O bonds in the trinuclear site. In this study, the two most plausible Cu-O structures of the trinuclear site, the tris-mu2-hydroxy-bridged and the mu3-oxo-bridged structures, are evaluated through spectroscopic and electronic structure studies on relevant model complexes, TrisOH and mu3O. It is found that the two components of a pseudo-A-term for TrisOH are associated with LMCT to the same Cu that are coupled by a metal-centered excited-state spin-orbit coupling (SOC), whereas for mu3O they are associated with LMCT to different Cu centers that are coupled by oxo-centered excited state SOC. Based on this analysis of the two candidate models, only the mu3-oxo-bridged structure is consistent with the spectroscopic properties of NI. The Cu-O sigma-bonds in the mu3-oxo-bridged structure would provide the thermodynamic driving force for the 4e- reduction of O2 and would allow the facile electron transfer to all Cu centers in the trinuclear cluster that is consistent with its involvement in the catalytic cycle.     

Spectroscopic and DFT investigation of [M{HB(3,5-iPr2pz)3}(SC6F5)] (M = Mn, Fe, Co, Ni, Cu, and Zn) model complexes: periodic trends in metal-thiolate bonding

A series of metal-varied [ML(SC6F5)] model complexes (where L = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate and M = Mn, Fe, Co, Ni, Cu, and Zn) related to blue copper proteins has been studied by a combination of absorption, MCD, resonance Raman, and S K-edge X-ray absorption spectroscopies. Density functional calculations have been used to characterize these complexes and calculate their spectra. The observed variations in geometry, spectra, and bond energies are interpreted in terms of changes in the nature of metal-ligand bonding interactions. The metal 3d-ligand orbital interaction, which contributes to covalent bonding in these complexes, becomes stronger going from Mn(II) to Co(II) (the sigma contribution) and to Cu(II) (the pi contribution). This change in the covalency results from the increased effective nuclear charge of the metal atom in going from Mn(II) to Zn(II) and the change in the 3d orbital populations (d5-->d10). Ionic bonding also plays an important role in determining the overall strength of the ML(+)-SC6F5(-) interaction. However, there is a compensating effect: as the covalent contribution to the metal-ligand bonding increases, the ionic contribution decreases. These results provide insight into the Irving-Williams series, where it is found that the bonding of the ligand being replaced by the thiolate makes a major contribution to the observed order of the stability constants over the series of metal ions.     

Performances et nouvelles possibilités de la microsonde électronique en spectrométrie des rayons X—I: Bandes d'émission Kβ5 du vanadium et de ses nitrures VN et VN0,82

Vanadium Kβ₅ emission bands from pure metal and nitrides VN and VN_0,82are investigated with an electron microprobe by automatic data collection and computer processing. Spectra are compared with the ones described previously. Their fine structure and the effects of the chemical bond are discussed in relation to the theories proposed in literature.     

Cyclopolymerisation. 6. Mitt. Darstellung und Eigenschaften von vernetzten cyclopolymerisierten Polyaminen.

Ohne Zusammenfassung