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Biomedical subjects

Y Henry

Publications and source records attributed to Y Henry.

At least 91 records · Page 5Linked to original sources
PubMed1984

Denitrification and nitrite reduction: Pseudomonas aeruginosa nitrite-reductase.

Present knowledge of the different enzymatic steps of the denitrification chains in various bacteria, particularly Paracoccus denitrificans and Pseudomonas aeruginosa has been briefly reviewed. The question whether nitric oxide (NO), nitrous oxide (N2O) and other nitrogen derivatives are obligatory intermediates has been discussed. The second part is an extensive review of the structure and the function of a key enzyme in denitrification, cytochrome c551-nitrite-oxidoreductase from P. aeruginosa. Recent results on the stoichiometry of nitrite reduction have been discussed.

Amino Acids↗
PubMed1984

Stoichiometry of nitrite reduction catalyzed by Pseudomonas aeruginosa nitrite-reductase.

The stoichiometry of the reduction of nitrite catalyzed by Pseudomonas aeruginosa nitrite-reductase (cytochrome cd1) has been shown to yield nitrous oxide as the final product. Gas chromatography experiments demonstrated that nitric oxide is also formed as a free intermediate. A sequential formation of NO and N2O is discussed as opposed to the parallel formation of the two products.

Chromatography, Gas↗
PubMed1982

Radical scavenging and electron-transfer reactions in Polyporus versicolor laccase a pulse radiolysis study.

The interaction of the radicals OH, t-BuO, Eaq, CO2 and O2 with the copper oxidase, laccase, from Polyporus, has been studied by the pulse-radiolysis technique. Each of these radicals formed transient adducts with a broad absorption maximum around 310 nm. Analysis of the optical properties and of the very fast rates of formation of these compounds shows that each radical interacts with a limited number of sites on the polypeptide part of the protein amongst R-S-S-R, histidine and aromatic residues. Interaction with the carbonyl group of some of the peptides bonds is also possible. The few target sites are probably hit simultaneously and electron transfer between these sites may also occur. In all cases, ina subsequent step, intramolecular electron transfer from the polypeptide radical adducts leads to a partial reduction of the blue type-1 Cu2+ with rates varying between 10(3) adn 10(4) s-1. Further reduction of the type-1 CU2+ occurs through a slow intermolecular reaction between two laccase radical transient adducts. In the case of CO2 and O2, this slow reduction could alternatively be due to an intermolecular reaction between laccase and CO2 or O2. The oxidation radicals OH, Br2 and (SCN)2, which formed radical adducts with fully ascorbate-reduced laccase, did not induce any type-1 copper reoxidation.

Butanols↗
PubMed1981

[Variations of nitrogen retention in the growing pig: effects on requirements].

The first part of this paper deals with the distribution of the protein fraction (total protein, amino acids) in the tissues and body compartments in the growing pig, according to age, growth potential (sex, genotype) and nutritional factors (feeding level). Overall protein retention is studied in the second part of the paper. The following points have been considered: changes in the protein retention curve during growth; variations according to the type of pig and nutrient supply; particular aspects of amino acid deposition with a relative constancy in the amino acid composition of deposited protein during the major part of growth. In the third part, the following consequences of variations in protein retention on protein requirement for growth have been analyzed: --relatively constant ratios between the requirements for individual essential amino acids and non-essential nitrogen (using lysine as a reference); --relation between protein (amino acid) requirement and level of protein deposition; --variations in the efficiency of utilization of dietary amino acids for growth, according to muscle growth potential and production objectives (final slaughter weight, type of pig and feeding program). The benefit of taking into consideration the components of apparent protein retention (synthesis and degradation) is discussed with a view to better adapting protein feeding to growth potential.

Amino Acids↗
PubMed1980

[Nitrite reduction by NADH, catalyzed by the nitrite reductase of Pseudomonas aeruginosa].

Reduction of nitrite by NADH catalyzed by Pseudomonas aeruginosa nitrite reductase is inhibited by a high concentration of nitric oxide NO. Contrary to what is currently admitted, we find that the nitrite reduction proceeds to the nitrogen monoxide N2O stage. EPR spectra show that, during the catalytic cycle, the enzyme forms specific Fe2+-NO heminic complexes.

Catalysis↗
PubMed1978

Photoreduction of copper chromophores in blue oxidases.

The low temperature (77 K) irradiation of oxidized ceruloplasmin and Rhus vernicifera laccase at the 330 nm absorption which arises from type 3 copper leads to the reduction of type 1 copper as demonstrated by bleaching of the 610 nm chromophore and the decrease of the EPR signal associated with this species. Type 2 copper remains unaffected. Concomitant with the type 1 copper reduction, a new EPR signal which is possibly that of a biradical appears. Upon thawing, type 1 copper is reversibly oxidized and the radical signal disappears. Irradiation of oxidized protein at the absorption band of type 1 copper produces no spectral change. An EPR study at room temperature confirms the wave-length specificity and reversibility of the photoreduction of type 1 copper and radical formation. Radical appearance and disappearance at room temperature are extremely slow (tau1/2 approximately 30 min). Optical studies at room temperature show that upon anaerobic irradiation of laccase in the 330 nm absorption band, both type 3 and type 1 chromophores are slowly reduced. Upon return to the dark and in the presence of O2, both type 3 and type 1 centers are reoxidized. Oxidizing equivalents either from O2 or K3Fe(CN)6 are required for the reoxidation reaction. These studies demonstrate that there is a direct energy transfer between type 3 and type 1 copper sites in blue copper oxidases.

Catechol Oxidase↗
PubMed1976

Binding of nitric oxide to reduced L-tryptophan-2,3-dioxygenase as studied by electron paramagnetic resonance.

Ferrous L-tryptophan-2,3-dioxygenase reacts with nitric oxide both in the presence and in the absence of L-tryptophan. Electron paramagnetic resonance studies suggest that the proximal ligand of the heme is a nitrogen atom, probably from an histidyl residue. The interaction of the protein with substrate changes both the symmetry of the paramagnetic center and the mode of interaction of the iron atom with its two axial ligands, NO and the proximal nitrogen atom. Optical absorption and EPR spectra suggest that the affinity of NO for tryptophan dioxygenase increases in the order: tryptophan dioxygenase, tryptophan dioxygenase + alpha-methyltryptophan, tryptophan diogenase " 5-hydroxytryptophan, tryptophan dioxygenase + L-tryptophan. A possible correlation between the number of superhyperfine lines in the EPR spectrum and the affinity of the enzyme for NO is discussed.

Binding Sites↗
PubMed1975

Heme reactivity of hemoglobins. Azide and fluoride binding equilibria of free and mercuriated ferri-gamma chains.

The free gamma chains, isolated from human foetal hemoglobin, are stable when oxidized and thus suitable for ligand binding and subunit equilibrium studies. The metaquo-ferri chains, with cysteine-F9 in the free state II ag gamma SH) possess several properties which are different from those of their p-mercuribenzoate derivative (III aq gammaSHgR); these are: stronger binding of a high-field ligand (N3- minus), altered spin equilibrium and an altered subunit equilibrium. A quantitative assessment of the free energy changes associated with all individual steps involved in changing the metaquo chains to their azide derivatives has been made. The results show that the higher apparent reactivity of III ag gammaSH (compared to IIIaq gammaSHgR) for the azide ion is not solely due to compensatory effects arising from differences of subunit dissociation or of spin equilibrium: other process(es) occurring in the ligand binding site have to be considered.

Azides↗