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Biomedical subjects

J Pommier

Publications and source records attributed to J Pommier.

At least 73 records · Page 4Linked to original sources
PubMed1984

Reduction of lactoperoxidase-H2O2 compounds by ferrocyanide: indirect evidence of an apoprotein site for one of the two oxidizing equivalents.

The titration by ferrocyanide and the localization of the oxidizing equivalents of lactoperoxidase "compound II" were studied as a function of pH. It was demonstrated that 1) whatever the pH, the structure of lactoperoxidase "compound II" was compatible with a Fe IV R degree state, 2) at acidic pH, ferrocyanide preferentially reduced the oxidizing equivalent localized on the heme iron to give an Fe III R degree compound, 3) at pH 4.2 only the Fe III R degree form was obtained after reduction of lactoperoxidase "compound II" with one mole of ferrocyanide and whereas at pH greater than 4.2, a mixture of both Fe III R degree and Fe IV R forms was present, 4) lowering the pH from 7.2 to 4.0 induced a transition of Fe IV R state to Fe III R degree state, but increasing the pH from 4.0 to 7.2 did not permit the formation of Fe IV R compound from Fe III R degree compound.

Apoenzymes↗
PubMed1984

A common pathway for the activation of several molybdoenzymes in Escherichia coli K12.

Three molybdoenzymes, nitrate reductase, formate benzyl-viologen oxidoreductase and trimethylamine-N-oxide reductase which form part of different systems, have been studied in a parental strain of Escherichia coli K12. When the organism is grown in the presence of 10 mM tungstate, these three enzymes are present in an inactive form which may be activated in vivo by the addition of 1 mM sodium molybdate. The mixing of soluble fractions from chlA and chlB mutants grown under the appropriate conditions leads to the activation of nitrate reductase, formate benzyl-viologen oxidoreductase and trimethylamine-N-oxide reductase. The activation of each enzyme is maximal when the mutants are grown under conditions that lead to the induction of that enzyme in the wild-type strain. The employment of purified proteins, the association factor FA and the Protein PA, which are presumed to be the products of the chlA and chlB genes, has shown that these proteins are responsible for the activation of the three enzymes during the complementation process.

Aldehyde Oxidoreductases↗
PubMed1984

NADPH-dependent H2O2 generation and peroxidase activity in thyroid particular fraction.

A NADPH-dependent H2O2 generating system associated with a thyroid particular fraction is described. H2O2 is measured by two different methods: iodination of NADPH itself when the system is supplemented with lactoperoxidase and [125I]iodide, and by the scopoletin method. It is shown that: H2O2 generation is inhibited by catalase and is dependent on NADPH or particulate protein concentration; radical scavengers of OH and of singlet oxygen have no effect while superoxide dismutase has only a marginal effect; disruption of the particular fraction by phospholipase A2 or digitonin treatment completely abolished H2O2 generation activity while thyroid peroxidase activity appears, suggesting different sites for the two activities in the membrane vesicles.

Animals↗
PubMed1980

Precursor forms of the subunits of nitrate reductase in chlA and chlB mutants of Escherichia coli K12.

The synthesis of nitrate reductase by a parental Escherichia coli K12 strain and its isogenic chlA and chlB mutants has been analyzed by protein double labelling with L-[4,5-3H]leucine and sulphur-35 and by immunoprecipitation using specific antiserum. The chlA and chlB mutants although defective in nitrate reductase activity retain the ability to synthesise the different polypeptides that are normally required for functional enzyme activity. In addition the data shows the following. 1. These polypeptides are present in unequal quantities in the membrane and in the cytoplasm of the cells. The chlB mutant synthesizes three times more nitrate reductase than the chlA mutant. 2. The subunit composition of the membrane-bound nitrate reductase present in the two mutants is different. 3. Membrane preparations from the chlB mutant contain the three subunits alpha, beta, gamma in a ratio which is similar to the wild type. 4. In the chlA mutant the two subunits beta and gamma are missing and the level of alpha subunit is very low. In the same membrane a 48,000-Mr subunit (polypeptide beta') precipitable by nitrate reductase antiserum has been found. The chlA and chlB mutants accumulate the three subunits alpha, beta and gamma in different proportion and concentrations in the cytoplasm unlike the parental strain. 5. The cytoplasm from the chlA mutant also contains the beta' polypeptide found in the membrane fraction of this mutant and in addition contain another polypeptide designated alpha' of molecular weight 105,000 which is precipitated by the nitrate reductase antiserum. The formation of particulate active nitrate reductase can be achieved by mixing the supernatant fractions of the chlA and chlB mutants (complementation) and procedes by two distinct but mutually dependent stages. Following reconstitution of activity the two peptides alpha' and beta' present in the supernatant fraction of the chlA mutant, disappear. Analysis of the immunoprecipitate polypeptides present in both the soluble and particulate nitrate reductase protein after reconstitution suggests that these polypeptides are precursors of the alpha and beta subunits following a process that remains to be elucidated.

Antigens, Bacterial↗
PubMed1980

Opposite effects of thiocyanate on tyrosine iodination and thyroid hormone synthesis.

The effect of a pseudohalide, SCN-, an anion with the same molecular size as iodide, was studied on two reactions: thyroglobulin iodination and thyroid hormone synthesis (coupling reaction) catalyzed by peroxidases. The coupling reaction was studied separately from the iodination reaction by using labelled thyroglobulin samples previously iodinated but containing little or no hormones. 1. SCN- inhibits iodide oxidation (I- leads to I2) whatever the enzyme, thyroid, lactoperoxidase or horseradish peroxidase. The amount of SCN- required to completely inhibit this reaction varies depending on the enzyme. Similarly tyrosine iodination is inhibited by SCN- with large variations, depending on the peroxidase, in the concentration of this anion required for inhibition. 2. In contrast SCN- stimulates the coupling reaction: (a) this affect is seen with the thyroid and lactoperoxidases but not with horseradish peroxidase; (b) the concentration of SCN- required for half-maximal stimulation of the coupling reaction is much lower (0.5-1 microM) than that required for the inhibition of iodide oxidation (60-80 microM); (c) ClO4(-), an anion with the same molecular size as SCN- and I-, has no effect on the coupling reaction; (d) this stimulatory effect of SCN- does not depend on a modification of the thyroglobulin molecule since it is not seen with horseradish peroxidase or in purely chemical coupling conditions. 3. The stimulatory effect of SCN- is therefore seen as resulting from the binding of this anion to a limited number of high-affinity sites present at the surface of both thyroid and lactoperoxidases. The inhibitory effect depends, in contrast, on the binding of SCN- to the substrate site with lower affinities. Since iodide also behaves both as a substrate for the iodination reaction and as a stimulatory ligand for the coupling reaction, these data provide further support in favour of the existence of an enzyme-iodide (or SCN-) complex with catalytic properties different from those of the native peroxidase.

Dose-Response Relationship, Drug↗
PubMed1979

Interaction of lactoperoxidase with thiols and diiodotyrosine.

Glutathione and cysteine bind to the heme of lactoperoxidase, thereby causing a red shift of the Soret band which is reversed upon addition of iodide or guaiacol, two substrates for lactoperoxidase. The rate of formation of the enzyme-thiol complex is enhanced by diiodotyrosine. Binding of diiodotyrosine to lactoperoxidase does not cause a shift of the Soret band which indicates binding to the protein of the enzyme. At neutral pH and low ionic strength, lactoperoxidase is adsorbed on insolubilized diiodotyrosine (diiodotyrosine-agarose). It can be eluted at slightly increased ionic strength which shows that the binding is weak. In the presence of 5 X 10(-4) M glutathione, however, the binding of the enzyme to diiodotyrosine-agarose becomes much stronger so that a high salt concentration is required for elution. Lactoperoxidase is also adsorbed on insolubilized thiols (thiol-agarose). The presence of diiodotyrosine is not required for strong binding. A simple method for the preparation of lactoperoxidase from milk by affinity chromatography is based on the interactions of the enzyme with the two ligands, thiols and diiodotyrosine.

Cysteine↗
PubMed1979

[Short- and mean results of mitral and aortic valve replacement with a Björk-Shiley disc prosthesis. Thromboembolic and hemorrhagic complications].

96 patients with a Björk aortic valve and 112 patients with a Björk mitral valve were followed up for four and a half years and five years after operation respectively. The actuarial survival rate was 82.5% in the aortic and 73% in the mitral patients. Late death was observed in 7.3% of mitral patients with thromboembolic complications and 4.2% of mitral patients with left ventricular dysfunction, compared to 2.6% of aortic patients with thromboembolism and 3.6% with left ventricular dysfunction. The incidence of thrombolic complications was three times as great with the prosthesis in the mitral position. The probability of absence of thromboembolic complications, studied by actuarial methods, was 93% at 4 1/2 years in aortic prostheses compared to 82% at 5 years in the mitral prostheses. 12 haemorrhagic complications (5.7%), with one fatality, were observed. Aortic valve replacement with a Björk prosthesis is a very satisfactory operation and the results compare favourably with other prostheses. However, the risk of thromboembolic complications should be seriously considered in the surgical indications when this prosthesis is to be used for mitral valve replacement.

Adolescent↗
PubMed1978

[In vitro synthesis of 3,5,3'-triiodothyronine catalyzed by thyroid peroxidase (author's transl)].

3,5,3'-triiodotyronine formation was studied in vitro after iodination of goiter thyroglobulin catalyzed by purified thyroid peroxidase. A fractionnal number of T3 is always obtained per mole of thyroglobulin in both in vitro and in vivo. This result cannot be explained by a heterogeneity in thyroglobulin iodination or in a partial conversion of T3 to T4. It is suggested that thyroglobulin is heterogenous either in its primary sequence or in its teritiary configuration. Thyroglobulin contains tyrosine residues which are specific for the T3 formation and moreover T3 is not the precursor of T4. The efficiency of T3 formation was studied: the maximal number of T3 molecules is obtained with 30 iodine atoms per mole of thyroglobulin. In addition the results suggest that the tyrosines which are coupled with a high efficiency are iodinated sequentially.

Catalysis↗
PubMed1977

Spatial requirement for coupling of iodotyrosine residues to form thyroid hormones.

A linear random copolymer of tyrosine and lysine and two synthetic oligopeptides containing two tyrosine residues in addition to lysine residues give thyroid hormone (thyroxine and triodothyronine) residues in good yield upon enzymatic iodination with thyroid peroxidase. These synthetic peptides may serve as simple models for thyroglobulin, the protein in which biosynthesis of the thyroid hormone takes place. For the formation of significant amounts of hormone, such model compounds must contain at least two properly spaced tyrosine residues.

Iodide Peroxidase↗