Extended X-ray absorption fine structure studies on periplasmic and intracellular molybdenum-binding proteins.

We have studied the molybdenum K-edge X-ray absorption spectra of Mo bound in the Mo-binding proteins Mop from Haemophilus influenzae, ModG from Azotobacter vinelandii and the Escherichia coli ModE transcriptional regulatory protein, and compared them with the absorption spectra of A. vinelandii ModA and monomeric molybdate. Pre-edge and extended fine structure data indicate that the Mo-binding proteins with molbindin-like domains bind tetrahedral molybdate with a Mo-O distance of 1.76 A. The molbindin subunits or sub-domains represent a novel protein fold that is used by proteins with distinct functions to bind molybdate in the cytoplasm. The high specificity of the proteins for molybdenum does not depend on a change of coordination number or geometry.

Synthesis, physicochemical properties, and biological evaluation of hydroxypyranones and hydroxypyridinones: novel bidentate ligands for cell-labeling.

The synthesis of a range of hydroxypyranones and hydroxypyridinones with potential for the chelation of indium(III) is described. The crystal structures of two of the indium complexes are presented. The distribution coefficients of the ligands and the corresponding iron(III), gallium(III), and indium(III) complexes are reported. Good linear relationships between the distribution coefficients of the iron and gallium complexes and iron and indium complexes were obtained. In contrast a nonlinear relationship was obtained between the distribution coefficient of the free ligand and the distribution coefficient of the three groups of complexes. This latter relationship was used to identify compounds with optimal cell labeling properties. Two such compounds both 6-(alkoxymethyl)-3-hydroxy-4H-pyran-4-ones have been compared with tropolone for their ability to label human leucocytes with 111In. The leucocyte labeling efficiencies of the selected ligands were greater and the in-vitro plasma stabilities were similar to that of 111In-tropolonate. These results suggest that the new bidentate ligands may offer advantages over those currently used for cell-labeling.