Characterization of metal ion-induced [3H]inositol hexakisphosphate binding to rat cerebellar membranes

The binding of [3H]inositol hexakisphosphate ([3H] InsP6) to rat cerebellar membranes has been characterized with the objective of establishing the role, if any, of a membrane protein receptor. In the presence of EDTA, we have previously identified an InsP6-binding site with a capacity of approximately 20 pmol/mg protein (Hawkins, P. T., Reynolds, D. J. M., Poyner, D. R., and Hanley, M. R. (1990) Biochem. Biophys. Res. Commun. 167, 819-827). However, in the presence of 1 mM Mg2+, the capacity of [3H]InsP6 binding to membranes was increased approximately 9-fold. This enhancing effect of Mg2+ was reversed by addition of 10 microM of several cation chelators, suggesting that the increased binding required trace quantities of other metal cations. This is supported by experiments where it was possible to saturate binding by addition of excess membranes, despite not significantly depleting radioligand, pointing to removal of some other factor. Removal of endogenous cations from the binding assay by pretreatment with chelex resin also prevents the Mg(2+)-induced potentiation. Consideration of the specificity of the chelators able to abolish this potentiation suggested involvement of Fe3+ or Al3+. Both these ions (but not several others) were able to increase [3H]InsP6 binding to chelex-pretreated membranes at concentrations of 1 microM. It is possible to demonstrate synergy between Fe3+ and Mg2+ under these conditions. We propose that [3H]InsP6 may interact with membranes through non-protein recognition possibly via phospholipids, in a manner dependent upon trace metals. The implications of this for InsP6 biology are considered.

Aller et venir:des verbes de déplacement aux auxiliaires aspectuels-temporels-modaux

Après avoir décrit le fonctionnement des verbes aller et venir, nous développons l’hypothèse selon laquelle leur grammaticalisation en auxiliaires s’effectue sur la base de l’élément spatial qui structure tant leur sémantisme commun – le déplacement vers une destination – que leur différence : l’orientation déictique (venir) / non déictique (aller) du déplacement. Nous testons cette hypothèse en analysant les principaux emplois des périphrases de structure [aller / venir (+prép.) + V(infinitif, gérondif)]. After a description of how movement verbs aller and venir work, we develop an hypothesis according to which their grammaticalisation into auxiliaries relies on the spatial element that structures their shared semantics – movement towards a destination - as well as their distinctive feature : a deictic (venir) or non deictic (aller) orientation of the movement. We test that hypothesis against an analysis of the main uses of periphrases in the [aller / venir (+ prep.) + V(infinitive, present participle)] pattern.