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At least 1,279 records · Page 71Linked to original sources
PubMed1984

The antibacterial action of Tinopal AN.

The bactericidal activity of Tinopal AN [1,1-bis(3,N-5-dimethyl-benzoxazol-2-yl)-methine p-toluene sulphonate] was shown to be due to a mechanism entirely independent of its inhibitory effects upon NADH dehydrogenase which were reported previously. Whereas the compound had no significant effect upon DNA synthesis in Escherichia coli D22, RNA and protein synthesis were immediately and markedly inhibited. In confirmation, Tinopal AN caused an immediate cessation in inducible beta-galactosidase synthesis in the same organism. An in vitro assay of the transcription of calf-thymus DNA by purified E. coli RNA polymerase showed that this process was inhibited by Tinopal AN.

Bacterial Proteins↗
PubMed2001

Map self-validation: a useful discriminator of phase correctness at low resolution.

A new map-validation procedure is based on the correlation-coefficient agreement between the observed structure-factor magnitudes and their extrapolated values from suitably modified electron-density maps from which they have been each in turn systematically excluded. The correlation coefficient tends to a maximum as the phase errors in a map are reduced. This principle was used to resolve the single-wavelength anomalous scattering (SAS) and single-derivative isomorphous replacement (SIR) phase ambiguity for a number of error-free trial structures. Applications employing real data sets tend to be more difficult owing to data incompleteness and errors affecting the construction of the Argand diagram.

Crystallography↗
PubMed2001

On the routine use of soft X-rays in macromolecular crystallography.

A diffraction data set has been collected from a blood coagulation factor XIII-Ca(2+) complex crystal at the X-ray diffraction beamline of the ELETTRA synchrotron (Trieste, Italy) at a wavelength of 2.6 A. The data collection could be carried out using the beamline as is, without making any time-consuming changes to the apparatus. Various data-processing schemes have been employed and it has been observed that local or detector scaling procedures are essential for producing the 'best' anomalous differences.

Crystallography, X-Ray↗
PubMed2001

A direct-method ab initio phasing of a protein, cupredoxin amicyanin, at 1.31 A resolution.

The direct-methods program MULTAN88 has been applied successfully to redetermine the structure of a protein, cupredoxin amicyanin, containing 808 non-H atom sites, one Cu atom and 132 ordered water molecules in the asymmetric unit using data at 1.31 A resolution. Starting with initially random phases, useful phase sets selected by figures of merit could be obtained from multiple trials. The E maps corresponding to the best eight phase sets in order of combined figures of merit (CFOM2) revealed a distorted tetrahedral geometry around the Cu site. The phase estimates from the metal and a few neighbouring atoms in the initial E map corresponding to the set with the highest CFOM2 could be improved by the density-modification procedure PERP and led to an interpretable electron-density map.

Azurin↗
PubMed1999

Evidence for a copper-coordinated histidine-tyrosine cross-link in the active site of cytochrome oxidase.

Following hints from X-ray data (Ostermeier C et al., 1997, Proc Natl Acad Sci USA 94:10547-10553; Yoshikawa S et al., 1998, Science 280: 1723-1729), chemical evidence is presented from four distantly related cytochrome-c oxidases for the existence of a copperB-coordinated His240-Tyr244) cross-link at the O2-activating Heme Fea3-CuB center in the catalytic subunit 1 of the enzyme. The early evolutionary invention of this unusual structure may have prevented damaging *OH-radical release at e(-)-transfer to dioxygen and thus have enabled O2 respiration.

Amino Acid Sequence↗
PubMed2004

Metabolic engineering of ketocarotenoid formation in higher plants.

Although higher plants synthesize carotenoids, they do not possess the ability to form ketocarotenoids. In order to generate higher plants capable of synthesizing combinations of ketolated and hydroxylated carotenoids the genes responsible for the carotene 4,4' oxygenase and 3,3' hydroxylase have been transformed into tomato and tobacco. The gene products were produced as a polyprotein. Subsequent cleavage of the polyprotein, targeting of the two enzymes to the plastid and enzyme activities have been shown for both gene products. Metabolite profiling has shown the formation of ketolated carotenoids from beta-carotene and its hydroxylated intermediates in tobacco and tomato leaf. In the nectary tissues of tobacco flowers a quantitative increase (10-fold) as well as compositional changes were evident, including the presence of astaxanthin, canthaxanthin and 4-ketozeaxanthin. Interestingly, in this tissue the newly formed carotenoids resided predominantly as esters. These data are discussed in terms of metabolic engineering of carotenoids and their sequestration in higher plant tissues.

Bacterial Proteins↗
PubMed1992

A comparative EPR investigation of the multicopper proteins nitrous-oxide reductase and cytochrome c oxidase.

The multicopper proteins, nitrous-oxide reductase (N2OR) and cytochrome c oxidase (COX), were investigated by EPR spectroscopy at microwave frequencies 2.4-35 GHz. Our results support a Cu-Cu interaction in COX and N2OR. At least 10 lines in the 2.7-GHz, 12 lines in the 4.6-GHz and 14 lines in the 9.2 GHz spectra were resolved for N2OR. Eight copper lines at 2.7 GHz, about nine lines at 4.6 GHz and about six lines at 9.2 GHz were resolved for COX. Simulations of the EPR spectra were consistent with most of the resonances of the multiline spectra, including regions in the center of the spectra where overlap of the three seven-line patterns is proposed. These simulations indicated that Cu-Cu interaction, in a mixed-valence [Cu(1.5) ... Cu(1.5)], S = 1/2 site is consistent with, if not proof of, the unusual spectral features observed for N2OR and COX.

Animals↗
PubMed1994

Purification and characterization of the periplasmic nitrate reductase from Thiosphaera pantotropha.

The periplasmic nitrate reductase of Thiosphaera pantotropha has been purified from a mutant strain (M-6) that overproduces the enzyme activity under anaerobic growth conditions. The enzyme is a complex of a 93-kDa polypeptide and a 16-kDa nitrate-oxidizable cytochrome c552. The complex contains molybdenum; a fluorescent compound with spectral features of a pterin derivative can be extracted. In contrast to the dissimilatory membrane-bound nitrate reductases, the periplasmic nitrate reductase shows high specificity for nitrate as a substrate and is insensitive to inhibition by azide. The 93-kDa subunit exhibits immunological cross-reactivity with the catalytic subunit of Rhodobacter capsulatus N22DNAR+ periplasmic nitrate reductase. Mass spectrometric comparisons of holo-cytochrome c552 and apo-cytochrome c552 demonstrated that the polypeptide bound two haem groups. Mediated redox potentiometry of the cytochrome indicated that the haem groups have reduction potentials (pH = 7.0) of approximately -15 mV and + 80 mV. The functional significance of these potentials is discussed in relation to the proposed physiological role of the enzyme as a redox valve.

Cell Membrane↗
PubMed1995

Purification and two-dimensional crystallization of bacterial cytochrome oxidases.

A novel strategy which employes chromatography on an immobilized metal ion has been developed for the purification of bacterial cytochrome c and quinol oxidases. Many bacterial oxidase complexes appear to have a natural affinity to bind to the chelated copper ion. A combination of three different chromatographic principles (anion exchange, metal-affinity and gel filtration) makes an effective tool chest for the preparation of homogeneous and protein-chemically pure bacterial oxidases. These preparations have been used for two-dimensional crystallization. Until now, crystals have been obtained using the Paracococcus denitrificans and Rhodobacter sphaeroides cytochrome aa3 and the Escherichia coli cytochrome bo. The crystals diffract to approximately 2.5 nm in negative stain and have potential for further structural studies.

Bacteria↗
PubMed2004

Optimization of an Escherichia coli system for cell-free synthesis of selectively N-labelled proteins for rapid analysis by NMR spectroscopy.

Cell-free protein synthesis offers rapid access to proteins that are selectively labelled with [15N]amino acids and suitable for analysis by NMR spectroscopy without chromatographic purification. A system based on an Escherichia coli cell extract was optimized with regard to protein yield and minimal usage of 15N-labelled amino acid, and examined for the presence of metabolic by-products which could interfere with the NMR analysis. Yields of up to 1.8 mg of human cyclophilin A per mL of reaction medium were obtained by expression of a synthetic gene. Equivalent yields were obtained using transcription directed by either T7 or tandem phage lambdapR and pL promoters, when the reactions were supplemented with purified phage T7 or E. coli RNA polymerase. Nineteen samples, each selectively labelled with a different 15N-enriched amino acid, were produced and analysed directly by NMR spectroscopy after ultracentrifugation. Cross-peaks from metabolic by-products were evident in the 15N-HSQC spectra of 13 of the samples. All metabolites were found to be small molecules that could be separated readily from the labelled proteins by dialysis. No significant transamination activity was observed except for [15N]Asp, where an enzyme in the cell extract efficiently converted Asp-->Asn. This activity was suppressed by replacing the normally high levels of potassium glutamate in the reaction mixture with ammonium or potassium acetate. In addition, the activity of peptide deformylase appeared to be generally reduced in the cell-free expression system.

Amino Acids↗
PubMed1974

Effect of the systemic fungicide carboxin on electron transport function in membranes of Micrococcus denitrificans.

The systemic fungicide carboxin (5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide) inhibited oxidation of succinate by membranes prepared from Micrococcus denitrificans, the K(i) being 16 muM. Oxycarboxin (5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide-4,4-dioxide), F831 (5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide-4-oxide), and another succinate oxidase inhibitor, 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (TTB) were less effective inhibitors of succinate oxidation by membranes of M. denitrificans. Oxidation of other substrates (nicotinamide adenine dinucleotide, reduced form, d-lactate, l-lactate, malate, and d,l-alpha-hydroxybutyrate) was inhibited to a lesser degree by carboxin, and formate oxidation was entirely resistant. With all substrates tested, oxycarboxin, the dioxide analogue of carboxin, was less effective than carboxin. Carboxin also inhibited dichlorophenol indophenol (DCIP) reductase activities by these membranes in a manner both qualitatively and quantitatively similar to the inhibition of oxidation of the various substrates. The inhibition of DCIP reductase activities by TTB was qualitatively similar to carboxin, but TTB was a less effective inhibitor with all substrates tested. The inhibition of DCIP reductase by carboxin could be relieved by phenazine methosulfate with all substrates except d-lactate. Only slight inhibition of d-lactate-stimulated uptake of [(14)C]glycine by these membrane vesicles was seen with carboxin. Uptake of [(14)C]glycine could be stimulated to varying degrees with the other substrates tested, but in no case did carboxin cause significant inhibition. Membranes isolated from M. denitrificans are a useful system for investigating the mechanism of inhibition of electron transport function by carboxin, and the use of this system for evaluations of carboxin and its metabolites is suggested.

Carboxin↗
PubMed1984

Heterotrophic nitrification among denitrifiers.

Twelve denitrifying bacteria representing six genera were tested for an ability to nitrify pyruvic oxime heterotrophically. Six of these bacteria exhibited appreciable nitrification activity, yielding as much as 5.8 mM nitrite and little or no nitrate when grown in a mineral salts medium containing 7 mM pyruvic oxime and 0.05% yeast extract. Of the six active bacteria, four (Pseudomonas denitrificans, Pseudomonas aeruginosa, and two strains of Pseudomonas fluorescens) could grow on yeast extract but not pyruvic oxime, one (Pseudomonas aureofaciens) could grow slowly on pyruvic oxime, and one (Alcaligenes faecalis) could apparently grow on pyruvic oxime in the presence of yeast extract but not in its absence. Eight of the twelve bacteria in the resting state could oxidize hydroxylamine to nitrite, and P. aureofaciens was remarkably active in this regard. In general, those denitrifiers active in the nitrification of pyruvic oxime or hydroxylamine or both are abundant in soils. A possible advantage of having nitrification and denitrification capabilities in the same organism is discussed.

Alcaligenes↗