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M Brune

Publications and source records attributed to M Brune.

107 records · Page 6Linked to original sources
PubMed1989

Iron absorption and phenolic compounds: importance of different phenolic structures.

The phenolic compounds (phenolic monomers, polyphenols, tannins) are considered to interfere with iron absorption by complex formation with iron in the gastro-intestinal lumen, making the iron less available for absorption. Very little is known about the extent to which different types of phenolic compounds of different size and chemical structure inhibit iron absorption. The relationship between iron absorption and the amount and type of phenolic compounds was studied by the extrinsic tag method. The aims of the studies were as follows: (i) To study the effect of small phenolic compounds with different hydroxylation patterns (gallic acid, catechin, chlorogenic acid) on iron absorption, (ii) To study the effect of different amounts of a hydrolysable tannin containing ten gallic acid residues (tannic acid) on iron absorption. (iii) To study the degree of inhibition of iron absorption by some foods and beverages (oregano, spinach, coffee and tea) in relation to their respective content of iron-binding phenolic groups, measured by a newly developed method. The inhibition of iron absorption by tannic acid was strongly dose-related. The smallest amount (5 mg) inhibited absorption by 20 per cent, 25 mg by 67 per cent and 100 mg by 88 per cent. Gallic acid inhibited iron absorption to the same extent as tannic acid, per mol galloyl groups, whereas no inhibition was observed when catechin was added to the test meal. Chlorogenic acid inhibited iron absorption to a lesser extent. Oregano and tea inhibited iron absorption in proportion to their respective content of galloyl groups, whereas the inhibitory effect of spinach was less marked. The inhibiting effect of coffee was explained mainly by its content of galloyl groups, but also by some other factor, probably chlorogenic acid. It is concluded that the content of iron-binding galloyl groups might be a major determinant of the inhibitory effect of phenolic compounds on iron absorption from the diet, whereas the phenolic catechol groups seem to be of minor importance. The results further suggest that the group of condensed tannins do not interfere with iron absorption.

Absorption↗
PubMed1988

Mutations in the nucleotide binding loop of adenylate kinase of Escherichia coli.

The adk gene of Escherichia coli has been used to overexpress the adenylate kinase protein in two ways: (1) by cloning the adk gene with its own promoter into pEMBL plasmids, which have an increased copy number, and (2) by deleting the adk promoter and cloning the gene behind the regulatable tac promoter. Adenylate kinase comprises up to 40% of the soluble cellular extracts from E. coli strains containing these plasmids. Mutations have been introduced into the gene by site-directed mutagenesis to exchange amino acids in the nucleotide binding loop, which is highly conserved in many mononucleotide binding proteins. The mutation of Lys13----Gln is nearly inactive, whereas the Pro9----Leu and the Gly10----Val mutant proteins have an increased Km for both substrates and a Vmax that is similar to wild type. Proton NMR measurements of the proteins show that a major structural change seems to have taken place for the Pro9----Leu and Gly10----Val mutants. The results are discussed in the light of the kinetic mechanism for adenylate kinase and the three-dimensional structure of the protein.

Adenylate Kinase↗
PubMed1988

Proton-nuclear magnetic resonance studies of the aromatic spin systems of Escherichia coli adenylate kinase.

Escherichia coli adenylate kinase has a very well resolved proton nuclear magnetic resonance spectrum in the region containing signals from aromatic amino acid side-chains. We found that the protein is structurally stable over a wide pH range and renatures spontaneously after acidic as well as basic denaturation. Only one out of the three histidyl imidazole rings titrates on changing the pH and has a pka value of 7.6. Two-dimensional nuclear magnetic resonance spectroscopy studies allowed use to identify most of the enzyme's aromatic spin systems, and by investigation of a mutant protein we were able to assign the aromatic part of the spin system of Tyr24 unambiguously.

Adenylate Kinase↗
PubMed1987

Infiltration of primary and metastatic melanomas with macrophages of the 25F9-positive phenotype.

In order to gain insight into the role of macrophages in human melanoma, we studied fresh-frozen material from 15 dysplastic nevi, 199 primary melanomas, 107 melanoma metastases, and paraffin sections from 98 primary melanomas with the monoclonal antibody 25F9 which recognizes an 86 x 10(3) dalton protein present on a subset of mature human macrophages. Considerable infiltration of tumors with 25F9-positive macrophages was observed in 2 dysplastic nevi (13%), 87 primary melanomas (44%), and 45 metastases (42%). The degree of intratumoral macrophage infiltration correlated with expression of class II HLA-DR antigens on tumor cells, in primary melanoma with a tumor thickness above 0.75 mm, and with the occurrence of metastases within 2 years. In paraffin sections, intratumoral 25F9-positive macrophages also correlated with metastatic spread of primary tumors after longer follow-up. Metastases revealed a higher degree of macrophage infiltration following systemic or local immunotherapy, compared with untreated metastases, or metastases removed during chemotherapy. Of 38 patients who died within an observation period of 1 year, 19 (50%) had considerable infiltration of metastases with 25F9-positive macrophages, whereas this was found in only 4 of 12 patients (33%), who survived for longer than 2 years following metastases removal. A higher degree of 25F9-positive macrophages correlated with a shift towards the T8-positive subsets within the T cell compartment of the infiltrate. Our results suggest that accumulation of 25F9-positive macrophages in melanomas indicates more aggressive tumor properties.

Antibodies, Monoclonal↗
PubMed1987

Is there a physiological role of vitamin C in iron absorption?

Nonheme iron usually constitutes more than 90% of the dietary iron. Its absorbability is a resultant of the balance between factors enhancing and inhibiting the absorption. Ascorbic acid is the most potent enhancer, and is the same for native and synthetic AA. The enhancing effect is strongly dose related (log dose/effect), and is different for different meals probably mainly due to varying content of inhibitors in the meals. AA also increases the iron absorption from simple meals with no known inhibitor, probably because AA impairs the formation of unavailable iron complexes with ligands normally present in the gastrointestinal lumen. The effect of AA is so unequivocal and marked that it must be considered as a physiological factor essential for the absorption of dietary iron.

Absorption↗
PubMed1986

Structural relationships in the adenylate kinase family.

The sequences of five distantly related adenylate kinases have been aligned. The local conservation of amino acids is discussed in the light of the known three-dimensional structure of one of the enzymes, the cytosolic isoenzyme 1 (AK1) from porcine muscle. The similarity profile outlines clearly the active site in the cleft of the spatial structure of AK1. The alignment reveals further that the enzyme family can be subdivided into small and large variants according to the presence or absence of a particular segment of about 30 residues in the middle of the chain. The extra segments of the large variants are strongly conserved.

Adenylate Kinase↗
PubMed1986

Low bioavailability of carbonyl iron in man: studies on iron fortification of wheat flour.

The bioavailability in man of commercially available elemental iron powders is unknown despite their extensive use for fortification of flour. Carbonyl iron, which is widely used in Europe, is considered as one of the best reduced iron powders based on studies both in vitro and in animals. In this study, a 55Fe labeled carbonyl iron was prepared by neutron irradiation and used to fortify wheat flour. The native iron of the wheat was extrinsically labeled by 59FeCl3. Doubly labeled wheat rolls were served with different meals. The ratio of absorbed 55Fe/59Fe is a direct measure of the fraction of carbonyl iron that joins the nonheme iron pool and is made potentially available for absorption. This relative bioavailability of carbonyl iron was unexpectedly low and varied from 20 to 5% when the iron fortified wheat rolls were served with different meals. The baking process did not change the relative bioavailability nor the addition of ascorbic acid. The low and variable bioavailability of carbonyl iron in man, makes it necessary to reconsider the rationale of using elemental iron powders for the fortification of foods for human consumption.

Adult↗
PubMed1986

Iron losses in sweat.

The losses of iron in whole body cell-free sweat were determined in eleven healthy men. A new experimental design was used with a very careful cleaning procedure of the skin and repeated consecutive sampling periods of sweat in a sauna. The purpose was to achieve a steady state of sweat iron losses with minimal influence from iron originating from desquamated cells and iron contaminating the skin. A steady state was reached in the third sauna period (second sweat sampling period). Iron loss was directly related to the volume of sweat lost and amounted to 22.5 micrograms iron/l sweat. The findings indicate that iron is a physiological constituent of sweat and derived not only from contamination. Present results imply that variations in the amount of sweat lost will have only a marginal effect on the variation in total body iron losses.

Adult↗
PubMed1986

Effect of ascorbic acid on iron absorption from different types of meals. Studies with ascorbic-acid-rich foods and synthetic ascorbic acid given in different amounts with different meals.

The effect of ascorbic acid on the absorption of non-heme iron was studied in 299 subjects. Different meals in which the non-heme iron was labelled with two different radio-iron isotopes were served with and without ascorbic acid to the same subject. Other meals containing foods with a known high content of ascorbic acid were also studied. Studies were also made giving different amounts of ascorbic acid with different meals. Marked differences in the enhancement of iron absorption were seen when ascorbic acid was given in different meals. It is suggested that ascorbic acid promotes iron absorption from the diet by reducing the negative effect on iron absorption of certain ligands such as phytates and tannins present in the diet. This interpretation is supported by observations that the most pronounced effects of ascorbic acid were found in meals with a high content of ligands known to inhibit iron absorption. Crystalline ascorbic acid and native ascorbic acid in foods appeared to have the same effect in promoting absorption of iron. The results indicate that ascorbic acid has a key physiologic role in facilitating the absorption of non-heme iron from the diet and that about 50 mg of the vitamin in each main meal is desirable for optimum effect.

Adult↗
PubMed1985

Cloning and sequencing of the adenylate kinase gene (adk) of Escherichia coli.

Adenylate kinase, the product of the adk locus in Escherichia coli K12, catalyzes the conversion of AMP and ATP to two molecules of ADP. The gene has been cloned by complementation of an adk temperature sensitive mutation. The DNA sequence of the complete coding region and of 5'- and 3'-untranslated regions were determined. The resulting protein sequence was found to contain several regions of high homology with cytosolic adenylate kinase of pig muscle (AK1), whose three-dimensional structure has been determined. The most significant of the amino acid exchanges is the replacement of histidine 36 with glutamine. This residue is believed to play a role in catalysis through metal ion binding. The codon usage pattern and the determination of adenylate kinase molecules per cell shows that the enzyme is one of the more abundant soluble proteins of the bacterial cells.

Adenylate Kinase↗
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Nursing↗