Probing interactions from solvent-exchangeable protons and monovalent cations with the 1,2-propanediol-1-yl radical intermediate in the reaction of dioldehydrase.

The reaction of adenosylcobalamin-dependent dioldehydrase with 1,2-propanediol gives rise to a radical intermediate observable by EPR spectroscopy. This reaction requires a monovalent cation such as potassium ion. The radical signal arises from the formation of a radical pair comprised of the Co(II) of cob(II)alamin and a substrate-related radical generated upon hydrogen abstraction by the 5'-deoxyadenosyl radical.

Environmental control of primary photochemistry in a mutant bacterial reaction center.

The core structure of the photosynthetic reaction center is quasisymmetric with two potential pathways (called A and B) for transmembrane electron transfer. Both the pathway and products of light-induced charge separation depend on local electrostatic interactions and the nature of the excited states generated at early times in reaction centers isolated from Rhodobacter sphaeroides. Here transient absorbance measurements were recorded following specific excitation of the Q(y)() transitions of P (the special pair of bacteriochlorophylls), the monomer bacteriochlorophylls (B(A) and B(B)), or the bacteriopheophytins (H(A) and H(B)) as a function of both buffer pH and detergent in a reaction center mutant with the mutations L168 His to Glu and L170 Asn to Asp in the vicinity of P and B(B).

Thermodynamic and EPR studies of slowly relaxing ubisemiquinone species in the isolated bovine heart complex I.

Previously, we investigated ubisemiquinone (SQ) EPR spectra associated with NADH-ubiquinone oxidoreductase (complex I) in the tightly coupled bovine heart submitochondrial particles (SMP). Based upon their widely differing spin relaxation rate, we distinguished SQ spectra arising from three distinct SQ species, namely SQ(Nf) (fast), SQ(Ns) (slow), and SQ(Nx) (very slow). The SQ(Nf) signal was observed only in the presence of the proton electrochemical gradient (deltamu(H)(+)), while SQ(Ns) and SQ(Nx) species did not require the presence of deltamu(H+).

Characterization of a small metal binding protein from Nitrosomonas europaea.

A small metal-binding protein (SmbP) with no known similarity to other proteins in current databases was isolated and characterized from the periplasm of Nitrosomonas europaea. The primary structure of this small (9.9 kDa) monomeric protein is characterized by a series of 10 repeats of a seven amino acid motif and an unusually high number of histidine residues.

A cambialistic superoxide dismutase in the thermophilic photosynthetic bacterium Chloroflexus aurantiacus.

Superoxide dismutase from the thermophilic anoxygenic photosynthetic bacterium Chloroflexus aurantiacus was cloned, purified, and characterized. This protein is in the manganese- and iron-containing family of superoxide dismutases and is able to use both manganese and iron catalytically. This appears to be the only soluble superoxide dismutase in C.

Synthesis of chlorophyll b: localization of chlorophyllide a oxygenase and discovery of a stable radical in the catalytic subunit.

Background: Assembly of stable light-harvesting complexes (LHCs) in the chloroplast of green algae and plants requires synthesis of chlorophyll (Chl) b, a reaction that involves oxygenation of the 7-methyl group of Chl a to a formyl group. This reaction uses molecular oxygen and is catalyzed by chlorophyllide a oxygenase (CAO). The amino acid sequence of CAO predicts mononuclear iron and Rieske iron-sulfur centers in the protein.

Evidence for a new metal in a known active site: purification and characterization of an iron-containing quercetin 2,3-dioxygenase from Bacillus subtilis.

The protein YxaG from Bacillus subtilis, of previously unknown function, was found to have quercetin 2,3-dioxygenase activity when overexpressed in Escherichia coli. The enzyme converts the flavonol quercetin to 2-protocatechuoylphloroglucinol carboxylic acid and carbon monoxide, indicating that it performs the same reaction and yields the same products as the well-characterized copper-containing quercetin 2,3-dioxygenase from Aspergillus. In contrast to the Aspergillus protein, YxaG contains iron, and the enzyme is sensitive to strong Fe(II) chelators, similar to the extensively studied catechol dioxygenases.

EPR and magnetic properties of heteronuclear Mn(n)Mg(6-)(n)(O(2)CNEt(2))(12): impact of structural distortions on Mn(II) in weak ligand fields.

The reaction between Mn(6)L(12) and Mg(6)L(12) (L = N,N-diethylcarbamate) results in isolation of heteronuclear complexes Mn(n)Mg(6)(-)(n)L(12). A series was prepared with different doping factors n by varying the Mn/Mg ratio in the crystallization solutions. Single-crystal X-ray diffraction shows that MnMg(5)L(12) is isostructural with Mn(6)L(12) and Mg(6)L(12).

Effects of heme ligand mutations including a pathogenic variant, H65R, on the properties of human cystathionine beta-synthase.

Human cystathionine beta-synthase is a hemeprotein that catalyzes a pyridoxal phosphate (PLP)-dependent condensation of serine and homocysteine into cystathionine. Biophysical characterization of this enzyme has led to the assignment of the heme ligands as histidine and cysteinate, respectively, which has recently been confirmed by crystal structure determination of the catalytic core of the protein. Using site-directed mutagenesis, we confirm that C52 and H65 represent the thiolate and histidine ligands to the heme.

Structural and Solution Characterization of Mononuclear Vanadium(IV) Complexes That Help To Elucidate the Active Site Structure of the Reduced Vanadium Haloperoxidases.

The complexes [VO(H(2)O)ada] (1), [VO(H(2)O)Hheida] (2), and [VO(H(2)O)aeida] (3) (H(2)ada, N-(carbamoylmethyl)iminodiacetic acid; H(3)heida, N-(2-hydroxyethyl)iminodiacetic acid; H(2)aeida, N-(2-aminoethyl)iminodiacetic acid) were synthesized and crystallographically characterized. Crystallographic parameters for 1.2H(2)O: monoclinic, space group P2(1)/c (No.