6 research outputs found
High-Resolution Analysis of Zn^2+ Coordination in the Alkaline Phosphatase Superfamily by EXAFS and X-ray Crystallography
Comparisons among evolutionarily related enzymes offer opportunities to reveal how structural differences produce different catalytic activities. Two structurally related enzymes, Escherichia coli alkaline phosphatase (AP) and
Xanthomonas axonopodis nucleotide pyrophosphatase/phosphodiesterase (NPP), have nearly identical binuclear Zn^2+ catalytic centers but show tremendous differential specificity for hydrolysis of phosphate monoesters or phosphate diesters. To determine if there are differences in Zn^2+ coordination in the two enzymes that might contribute to catalytic specificity, we analyzed both x-ray absorption spectroscopic and x-ray
crystallographic data. We report a 1.29-Å crystal structure of AP with bound phosphate, allowing evaluation of interactions at the AP metal site with high resolution. To make systematic comparisons between AP and NPP, we measured zinc extended x-ray absorption fine structure for AP and
NPP in the free-enzyme forms, with AMP and inorganic phosphate groundstate analogs and with vanadate transition-state analogs. These studies yielded average zinc–ligand distances in AP and NPP free-enzyme forms
and ground-state analog forms that were identical within error, suggesting little difference in metal ion coordination among these forms. Upon binding of vanadate to both enzymes, small increases in average metal–ligand distances were observed, consistent with an increased coordination number. Slightly longer increases were observed in NPP relative to AP, which could arise from subtle rearrangements of the active site or differences in the geometry of the bound vanadyl species. Overall, the
results suggest that the binuclear Zn^2+ catalytic site remains very similar between AP and NPP during the course of a reaction cycle
НАПРАВЛЕНИЯ СОВЕРШЕНСТВОВАНИЯ ОБРУДОВАНИЯ ДЛЯ ФЛОТАЦИОННОГО ОБОГАЩЕНИЯ ТОНКОДИСПЕРСНыХ МАТЕРИАЛОВ
Проблема и ее связь с научными и практическими задачами. В связи с тем, что в поступающем на обогатительные фабрики сырье содержится до 30% ма-териала крупностью менее 1 мм, роль процесса флотации существенно возрас-тает. Этому способствует и возможность создания достаточно простых замкну-тых водно-шламовых схем, включающих флотацию в качестве основного эле-мента очистки оборотных вод. Многими исследованиями, которые проводились ранее и продолжают выполняться и в настоящее время, установлены направле-ния совершенствования этого достаточно сложного физико-химического про-цесс
High-Resolution Analysis of Zn2+ Coordination in the Alkaline Phosphatase Superfamily by EXAFS and X-ray Crystallography
Bis(μ-oxo) Dicopper(III) Species of the Simplest Peralkylated Diamine: Enhanced Reactivity toward Exogenous Substrates
Revisiting the Polyoxometalate-Based Late-Transition-Metal-Oxo Complexes: The “Oxo Wall” Stands
Terminal oxo complexes of the late transition metals Pt, Pd, and
Au have been reported by us in <i>Science</i> and <i>Journal of the American Chemical Society</i>. Despite thoroughness
in characterizing these complexes (multiple independent structural
methods and up to 17 analytical methods in one case), we have continued
to study these structures. Initial work on these systems was motivated
by structural data from X-ray crystallography and neutron diffraction
and <sup>17</sup>O and <sup>31</sup>P NMR signatures which all indicated
differences from all previously published compounds. With significant
new data, we now revisit these studies. New X-ray crystal structures
of previously reported complexes K<sub>14</sub>[P<sub>2</sub>W<sub>19</sub>O<sub>69</sub>(OH<sub>2</sub>)] and “K<sub>10</sub>Na<sub>3</sub>[Pd<sup>IV</sup>(O)(OH)WO(OH<sub>2</sub>)(PW<sub>9</sub>O<sub>34</sub>)<sub>2</sub>]” and a closer examination of
these structures are provided. Also presented are the <sup>17</sup>O NMR spectrum of an <sup>17</sup>O-enriched sample of [PW<sub>11</sub>O<sub>39</sub>]<sup>7–</sup> and a careful combined <sup>31</sup>P NMR-titration study of the previously reported “K<sub>7</sub>H<sub>2</sub>[Au(O)(OH<sub>2</sub>)P<sub>2</sub>W<sub>20</sub>O<sub>70</sub>(OH<sub>2</sub>)<sub>2</sub>].” These and considerable
other data collectively indicate that previously assigned terminal
Pt-oxo and Au-oxo complexes are in fact cocrystals of the all-tungsten
structural analogues with noble metal cations, while the Pd-oxo complex
is a disordered Pd(II)-substituted polyoxometalate. The neutron diffraction
data have been re-analyzed, and new refinements are fully consistent
with the all-tungsten formulations of the Pt-oxo and Au-oxo polyoxometalate
species