The 2-Ga peraluminous magmatism of the Jacobina-Contendas Mirante belts (Bahia, Brazil) : geologic and isotopic constraints on the sources

L'étude pétrographique des intrusions granitiques du craton Sao Francisco (Bahia, Brésil) permet de définir la chronologie absolue des épisodes magmatiques et d'identifier les sources magmatiques ainsi que les processus géodynamiques se produisant lors de l'orogenèse transamazonienn

The Quaternary Structure of the R-State of Escherichia coli Aspartate Transcarbamoylase in Solution Is Different from That in the Crystal and Is Modified by Mg 2+ ·ATP Binding

International audienc

Interactions in solution of a large oligomeric protein

International audienceUp to now, systematic studies on protein interactions in solution have been (mostly) restricted to small molecular weight model proteins like lysozyme, BPTI or gamma-crystallins. Those studies involving a combination of techniques (osmotic pressure, light scattering, small-angle X-ray scattering, etc.) led to an interpretation of the results in terms of interaction potentials, the parameters of which can be related in a semi-quantitative way to van der Waals forces and particle charges. We have undertaken an X-ray scattering study to extend the interaction potential analysis to the case of a large size oligomeric protein, aspartate transcarbamylase from E. coli. This heterododecamer comprises two trimers of catalytic chains and three dimers of regulatory chains for a total molecular weight of 306 kDA. It is a slightly acidic protein (pI = 5.9). The main thermodynamic and chemical parameters were varied: temperature, protein concentration, pH, salt nature and concentration. Moreover, we took advantage of the large molecular weight of ATCase to study the effect of polyethylene glycols. The results are compared to those reached in the case of small proteins. (C) 1999 Elsevier Science B.V. All rights reserved

The 2-Ga peraluminous magmatism of the Jacobina-Contendas Mirante belts (Bahia, Brazil) : geologic and isotopic constraints on the sources

L'étude pétrographique des intrusions granitiques du craton Sao Francisco (Bahia, Brésil) permet de définir la chronologie absolue des épisodes magmatiques et d'identifier les sources magmatiques ainsi que les processus géodynamiques se produisant lors de l'orogenèse transamazonienn

Comparative structural analysis of low-molecular mass fragments of Rapana venosa hemocyanin obtained using two different procedures

Different fragments of the hemocyanin (Hc) isolated from the gastropod Rapana venosa containing a single functional unit (50 kDa), two functional units (100 kDa) and three functional units (150 kDa) were obtained in a dissociating buffer in the presence of Zn2+ and purified to homogeneity. Their conformations in solution were studied by means of small angle X-ray scattering (SAXS) and compared with those of the corresponding fragments previously obtained by limited proteolysis [Arch. Biochem. Biophys., 2000, 373, 154]. The overall shape of each fragment was determined using an ab initio approach. The crystal structures of the functional unit e from the same Hc and from another molluscan Hc (Octopus dofleini) were used to model 100 and 150 kDa fragments using rigid body movements to fit the corresponding SAXS patterns. Interesting differences were observed between the functional unit organization in the low-molecular mass fragments according to the two preparation methods, suggesting different localizations within the 11S functional subunit.[...