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O2 Binding (o2 + binding)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

A novel thermostable hemoglobin from the actinobacterium Thermobifida fusca

FEBS JOURNAL, Issue 16 2005
Alessandra Bonamore
The gene coding for a hemoglobin-like protein (Tf-trHb) has been identified in the thermophilic actinobacterium Thermobifida fusca and cloned in Escherichia coli for overexpression. The crystal structure of the ferric, acetate-bound derivative, was obtained at 2.48 Å resolution. The three-dimensional structure of Tf-trHb is similar to structures reported for the truncated hemoglobins from Mycobacterium tuberculosis and Bacillus subtilis in its central domain. The complete lack of diffraction patterns relative to the N- and C-terminal segments indicates that these are unstructured polypeptides chains, consistent with their facile cleavage in solution. The absence of internal cavities and the presence of two water molecules between the bound acetate ion and the protein surface suggest that the mode of ligand entry is similar to that of typical hemoglobins. The protein is characterized by higher thermostability than the similar mesophilic truncated hemoglobin from B. subtilis, as demonstrated by far-UV CD melting experiments on the cyano-met derivatives. The ligand-binding properties of Tf-trHb, analyzed in stopped flow experiments, demonstrate that Tf-trHb is capable of efficient O2 binding and release between 55 and 60 °C, the optimal growth temperature for Thermobifida fusca. [source]

Near-stoichiometric O2 binding on metal centers in Co(salen) nanoparticles

AICHE JOURNAL, Issue 4 2009
Chad Johnson
Abstract Co(salen) [cobaltous bis(salicylaldehyde)ethylenediamine] complexes are well-known O2 carriers in solution. In the solid phase, these complexes exhibit some O2 binding but detailed studies have been complicated because few of the known polymorphs of Co(salen) actually bind O2. The O2 binding results for nanoparticulate Co(salen) are presented in this study. Rod-shaped Co(salen) nanoparticles, roughly 100 nm in diameter, were recrystallized by spraying a methylene chloride solution of commercially obtained Co(salen) into supercritical carbon dioxide. Temperature-programmed desorption, thermogravimetric analysis, and a Rubotherm magnetic suspension balance measurements reveal a reversible O2 uptake of ,1.51 mmol/(g nanoparticles) at 25°C, consistent with a binding stoichiometry involving a bridging peroxo unit between two Co centers. In contrast, no measurable O2 uptake was observed with the commercial Co(salen). These results clearly show the potential for bottom-up design of nanoparticulate metal complexes for enhanced O2 storage and other applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Review: Correlations between oxygen affinity and sequence classifications of plant hemoglobins,

BIOPOLYMERS, Issue 12 2009
Benoit J. Smagghe
Abstract Plants express three phylogenetic classes of hemoglobins (Hb) based on sequence analyses. Class 1 and 2 Hbs are full-length globins with the classical eight helix Mb-like fold, whereas Class 3 plant Hbs resemble the truncated globins found in bacteria. With the exception of the specialized leghemoglobins, the physiological functions of these plant hemoglobins remain unknown. We have reviewed and, in some cases, measured new oxygen binding properties of a large number of Class 1 and 2 plant nonsymbiotic Hbs and leghemoglobins. We found that sequence classification correlates with distinct extents of hexacoordination with the distal histidine and markedly different overall oxygen affinities and association and dissociation rate constants. These results suggest strong selective pressure for the evolution of distinct physiological functions. The leghemoglobins evolved from the Class 2 globins and show no hexacoordination, very high rates of O2 binding (,250 ,M,1 s,1), moderately high rates of O2 dissociation (,5,15 s,1), and high oxygen affinity (Kd or P50 , 50 nM). These properties both facilitate O2 diffusion to respiring N2 fixing bacteria and reduce O2 tension in the root nodules of legumes. The Class 1 plant Hbs show weak hexacoordination (KHisE7 , 2), moderate rates of O2 binding (,25 ,M,1 s,1), very small rates of O2 dissociation (,0.16 s,1), and remarkably high O2 affinities (P50 , 2 nM), suggesting a function involving O2 and nitric oxide (NO) scavenging. The Class 2 Hbs exhibit strong hexacoordination (KHisE7 , 100), low rates of O2 binding (,1 ,M,1 s,1), moderately low O2 dissociation rate constants (,1 s,1), and moderate, Mb-like O2 affinities (P50 , 340 nM), perhaps suggesting a sensing role for sustained low, micromolar levels of oxygen. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 1083,1096, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]

A Novel Tripodal Ligand Containing Three Different N -Heterocyclic Donor Functions and Its Application in Catechol Dioxygenase Mimicking

CHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2009
Marit Wagner Dipl.-Chem.
Abstract Prominent donors: A pyridyl, an imidazolyl, and a pyrazolyl donor function are part of the novel tripodal ligand depicted, which thus combines three of the most prominent donors applied in ligands for bioinorganic chemistry within one coordination unit. To exploit its behaviour and potential, first investigations have been carried out in relation to catechol dioxygenase mimicry. We describe a novel chiral ligand, L, in which three different N -donor functions are linked to a methoxymethine unit: a methylpyrazole derivative, a methylimidazole unit, and a pyridyl residue. Complexes with FeCl2, FeBr2, and FeCl3 have been synthesized and fully characterized, including with respect to their molecular structures. While in combination with FeCl3L coordinates in a tripodal fashion, with FeX2 (X=Cl, Br) it binds only through two functions and the pyridyl unit remains dangling. For potential modelling of intradiol and extradiol catechol dioxygenase reactivity, the complexes [LFeCl2], 1, and [LFeCl3], 3, have been treated with 3,5-di- tert -butylcatechol, triethylamine, and O2. Both complexes yielded similar results in such investigations, since the LFeII,catecholate complex reacts with O2 through one-electron oxidation in the first step. Employing 3 in acetonitrile solution, intradiol cleavage occurred, although the undesired quinone was formed as the main product. If reagents were added (NaBPh4, H+) or reaction conditions were chosen (CH2Cl2 instead of CH3CN as the solvent) that made the coordination sphere at the iron centre more accessible for a third substrate donor function, an alternative reaction route, presumably involving O2 binding at the metal, became more important, which led to extradiol cleavage. In the extreme case (CH2Cl2 as the solvent and with the addition of NaBPh4), mainly the extradiol cleavage products were formed; the intradiol products were only observed as side products then and quinone formation became negligible. Protonated base functions in the second coordination sphere increased the efficiency of extradiol cleavage only slightly. The obtained results are in line with current understanding of the function of intradiol/extradiol dioxygenases. [source]