Metal-insulator transition in Ca_{1-x}Li_xPd_3O_4

Metal-insulator transition in Ca_{1-x}Li_xPd_3O_4 has been studied through charge transport measurements. The resistivity, the Seebeck coefficient, and the Hall coefficient are consistently explained in terms of a simple one-band picture, where a hole with a moderately enhanced mass is itinerant three-dimensionally. Contrary to the theoretical prediction [Phys. Rev. B62, 13426 (2000)], CaPd_3O_4 is unlikely to be an excitonic insulator, and holds a finite carrier concentration down to 4.2 K. Thus the metal-insulator transition in this system is basically driven by localization effects.Comment: RevTeX4 format, 4 pages, 5 eps figure

Remodeling of the AB site of rat parvalbumin and oncomodulin into a canonical EF-hand

Parvalbumin (PV) and the homologous protein oncomodulin (OM) contain three EF-hand motifs, but the first site (AB) cannot bind Ca2+. Here we aimed to recreate the putative ancestral proteins [D19-28E]PV and [D19-28E]OM by replacing the 10-residue-long nonfunctional loop in the AB site by a 12-residue canonical loop. To create an optical conformational probe we also expressed the homologs with a F102W replacement. Unexpectedly, in none of the proteins did the mutation reactivate the AB site. The AB-remodeled parvalbumins bind two Ca2+ ions with strong positive cooperativity (nH = 2) and moderate affinity ([Ca2+]0.5 = 2 microM), compared with [Ca2+]0.5 = 37 nM and nH = 1 for the wild-type protein. Increasing Mg2+ concentrations changed nH from 2 to 0.65, but without modification of the [Ca2+]0. 5-value. CD revealed that the Ca2+ and Mg2+ forms of the remodeled parvalbumins lost one-third of their alpha helix content compared with the Ca2+ form of wild-type parvalbumin. However, the microenvironment of single Trp residues in the hydrophobic cores, monitored using intrinsic fluorescence and difference optical density, is the same. The metal-free remodeled parvalbumins possess unfolded conformations. The AB-remodeled oncomodulins also bind two Ca2+ with [Ca2+]0.5 = 43 microM and nH = 1.45. Mg2+ does not affect Ca2+ binding. Again the Ca2+ forms display two-thirds of the alpha-helical content in the wild-type, while their core is still strongly hydrophobic as monitored by Trp and Tyr fluorescence. The metal-free oncomodulins are partially unfolded and seem not to possess a hydrophobic core. Our data indicate that AB-remodeled parvalbumin has the potential to regulate cell functions, whereas it is unlikely that [D19-28E]OM can play a regulatory role in vivo. The predicted evolution of the AB site from a canonical to an abortive EF-hand may have been dictated by the need for stronger interaction with Mg2+ and Ca2+, and a high conformational stability of the metal-free forms