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Biomedical subjects

L Petersson

Publications and source records attributed to L Petersson.

34 records · Page 2Linked to original sources
PubMed1987

Magnetic interaction between the tyrosyl free radical and the antiferromagnetically coupled iron center in ribonucleotide reductase.

Ribonucleotide reductases from Escherichia coli and from mammalian cells are heterodimeric enzymes. One of the subunits, in the bacterial enzyme protein B2 and in the mammalian enzyme protein M2, contains iron and a tyrosyl free radical that both are essential for enzyme activity. The iron center in protein B2 is an antiferromagnetically coupled pair of high-spin ferric ions. This study concerns magnetic interaction between the tyrosyl radical and the iron center in the two proteins. Studies of the temperature dependence of electron paramagnetic resonance (EPR) relaxation and line shape reveal significant differences between the free radicals in proteins B2 and M2. The observed temperature-dependent enhanced EPR relaxation and line broadening of the enzyme radicals are furthermore completely different from those of a model UV-induced free radical in tyrosine. The results are discussed in terms of magnetic dipolar as well as exchange interactions between the free radical and the iron center in both proteins. The free radical and the iron center are thus close enough in space to exhibit magnetic interaction. For protein M2 the effects are more pronounced than for protein B2, indicating a stronger magnetic interaction.

Animals↗
PubMed1987

Extended X-ray absorption fine structure studies on the iron-containing subunit of ribonucleotide reductase from Escherichia coli.

Iron K-edge X-ray absorption spectra were obtained on the protein B2, the small subunit of ribonucleotide reductase from Escherichia coli. Protein B2 contains a binuclear iron center with many properties in common with the iron center of oxidized hemerythrins. The extended X-ray absorption fine structure (EXAFS) measurements on protein B2 were analyzed and compared with published data for oxyhemerythrin. In protein B2 there are, in the first coordination shell around each Fe atom, five or six oxygen or nitrogen atoms that are directly coordinated ligands. In oxyhemerythrin there are six ligands to each iron. As in oxyhemerythrin, one of the ligands in the first shell of protein B2 is at a short distance, about 1.78 A, confirming the existence of a mu-oxo bridge. The other atoms of the first shell are at an average distance of 2.04 A, which is about 0.1 A shorter than in oxyhemerythrin. In protein B2 the Fe-Fe distance is in the range 3.26-3.48 A, and the bridging angle falls between 130 and 150 degrees. On the basis of these data, there is no direct evidence for any histidine ligands in protein B2, but the noise level leaves way for the possibility of a maximum of about three histidines for each Fe pair. The X-ray absorption spectrum of a hydroxyurea-treated sample was not significantly different from that of the native protein B2, which implies that no significant alteration in the structure of the iron site occurs upon destruction of the tyrosine radical.

Escherichia coli↗
PubMed1985

Fluorine levels in in vitro remineralized enamel after treatment with 1000 ppm F as NaF, MFP or mixed solutions.

By means of secondary ion mass spectrometry (SIMS) an investigation has been made of the F uptake and the transport of fluorine-carrying ions in artificially carious human enamel after in vitro remineralization. The fluoridation was effected from solutions of pure Na2FPO3 (MFP), pure NaF, or mixtures of MFP and NaF, always with a total F content of 1000 atom-ppm. The recorded in depth profiles of F concentration show that, after 14 days of remineralization, 1) neither the acquired F levels nor the F distributions are greatly dependent on whether fluoridation is from NaF, MFP or mixtures, 2) the F distribution shape is not strongly influenced by a 3-month storage followed by remineralization, 3) the penetration of F beyond the lesion is generally deeper from NaF than from MFP, and 4) the effect of long storage on penetration depth is mainly noticeable for MFP-treated specimens.

Adult↗
PubMed1982

Caries increment in primary teeth after application of Duraphat fluoride varnish.

In order to evaluate the possible cariostatic effect of a fluoride varnish in the primary dentition, Duraphat varnish was applied twice yearly for 2 years to the teeth of 195 3 1/2-year-old children of both sexes attending nine preparatory schools in the Warsaw area. A control group of 127 children attending nine other preparatory schools was also examined. For each child a dmfs1 index (including "caries without macroscopic defect") and a dmfs2 index ("caries without macroscopic defect" excluded) were determined as well as a dmft1 and a dmft2 index. After 2 years the difference between the test and the control groups regarding the mean dmfs1 and dmft2 index increments was 9.39% (P greater than 0.1) and 24.09% (P less than 0.05), respectively. No significant differences were found, however, concerning the dmft2 and dmfs2 indices, the percentage children with new gingival caries, the number of teeth extracted on account of caries and the number of remaining teeth. A test group of 46 children treated with fluoride varnish in which a complete radiological examination could be carried out before and after the experimental period and which was treated with fluoride varnish was compared with a similar group of 27 children, which was not treated with fluoride varnish. The differences in caries increments were small, less than 15%, and were not significant. Taking into consideration the great variation between the schools it was concluded that the cariostatic effect of Duraphat application twice yearly in the primary dentition of these children was slight.

Child, Preschool↗
PubMed1980

The iron center in ribonucleotide reductase from Escherichia coli.

Ribonucleotide reductase from Escherichia coli consists of two nonidentical subunits, proteins B1 and B2. The active site is made up from both subunits. Protein B2 contains 2 iron atoms and a tyrosyl-free radical, which are essential for the enzymatic activity. The paramagnetic susceptibility of protein B2 has been measured over the temperature range 30-200 K. A deviation from the Curie law is observed at high temperatures, consistent with a structure of an antiferromagnetically coupled pair of high spin Fe(III) with an exchange coupling -J = 108(-20)+25 cm-1. Electronic spectra are resolved into components from the iron center and the radical. A band at 600 nm is clearly identified and shown to have contributions from both components. The electronic absorptions of the tyrosyl radical of protein B2 are closely similar to those reported for phenoxy radicals of tyrosine and tritertiary butyl phenol. Determinations by EPR of the amount of free radical suggest the possibility of more than one radical per active protein B2 molecule. Reconstitution of the active site from apoprotein B2 and Fe(II) is only observed in the presence of oxygen. With Fe(III), no reconstitution is obtained. The additional physical data on the iron center of protein B2 strengthen the analogy with oxidized forms of hemerythrin. The most likely structure is an antiferromagnetically coupled pair of high spin Fe(III), possibly with a bridging oxo-group.

Aerobiosis↗
PubMed1980

Antiferromagnetic exchange interaction in the two-iron-two-sulphur ferredoxin from the blue-green alga Spirulina maxima studied with a highly sensitive magnetic balance.

1. A highly sensitive magnetic balance of the Faraday type is described. 2. The magnetic susceptibility of the oxidized and reduced forms of the two-iron-two-sulphur ferredoxin from the blue-green alga Spirulina maxima has been measured over a wide temperature range. 3. The results can be interpreted within a simple model involving antiferromagnetically coupled iron atoms at the active site. The coupling, expressed as --J, is estimated to be 182 +/- 20/cm and 98 +5/-10 /cm for the oxidized and reduced forms, respectively.

Binding Sites↗
PubMed1980

Electron paramagnetic resonance of the copper in dopamine beta-monooxygenase. Rapid reduction by ascorbate, the steady-state redox level, chelation with EDTA, and reactivation of the apoenzyme by added copper.

The water-soluble form of dopamine beta-monooxygenase from bovine adrenal medulla was studied. Addition of excess CuSO4 to purified enzyme preparations followed by extensive ultrafiltration against copper-free buffer at pH 7.0, gave preparations with about four copper atoms per enzyme tetramer of Mr 290 000. The enzyme-bound copper was shown by the rapid-freeze technique and electron paramagnetic resonance (EPR) to be reduced by ascorbate at a rate which was faster than the overall catalytic rate; about 10% of the copper was oxidized to Cu(II) during steady-state catalysis in the presence of excess ascorbate. These results support an electron-transfer function of the enzyme-bound copper during catalysis and indicate that the reduction by ascorbate is not the rate-limiting step. The enzyme-bound copper was rapidly chelated by EDTA at pH 7.0., and the apoenzyme thus obtained after dialysis revealed no EPR-detectable copper. Addition of CuSO4 to the apoenzyme gave an EPR spectrum similar to that of the native enzyme, and the apoenzyme was fully reactivated by the optimal concentration of CuSO4 in less than 2 s.

Adrenal Medulla↗
PubMed1978

Magnetic susceptibility of laccases and ceruloplasmin.

1. Recent magnetic susceptibility measurements on laccase (monophenol,dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) from the lacquer tree Rhus vernicifera showed a deviation from Curie behaviour above 50 K, which was taken as evidence for an antiferromagnetically coupled Cu(II)-Cu(II) pair in the oxidized enzyme. The magnetic susceptibility of this protein has been reinvestigated. Further measurements on laccase from the fungus Polyporus versicolor and human ceruloplasmin (iron(II):oxygen oxidoreductase, EC 1.16.3.1) are presented. 2. The magnetic susceptibility of fungal laccase and lacquer tree laccase can be accounted for by the EPR detectable copper ions in the temperature range 40--300 K. 3. If an antiferromagnetically coupled Cu(II)-Cu(II) pair exists in the laccases, then the coupling, expressed as --J, should be at least of the order of 300 cm-1, as deduced from the Curie dependence of the susceptibility and the sensitivity in our measurements. 4. If an analogy with the laccases is assumed for the EPR invisible copper in ceruloplasmin then a limiting value of the coupling may be deduced also in this case, with --J at least of the order of 200 cm-1.

Catechol Oxidase↗
PubMed1975

The iron electron-nuclear double resonance (ENDOR) of 4-Fe clusters in iron-sulfur proteins from Chromatium and Clostridium pasteurianum.

Iron electron-nuclear double resonance (ENDOR) measurements were made of the 4-Fe clusters in oxidized Chromatium high-potential iron-sulfur protein, dithionite-reduced high-potential iron-sulfur protein in 80% dimethylsulphoxide, fully reduced Clostridium pasteurianum ferredoxin in aqueous solution and in 80% dimethylsulfoxide. The hyperfine couplings determined show that: i) the electron distribution in each case is nearly symmetric; ii) there are two types of iron in oxidized high potential iron-sulfur protein; iii) only one type of iron is observed in each fully reduced 4-Fe cluster; iv) the data also suggest a greater electron delocalization onto the ligands as compared to the 2-Fe ferredoxins.

Bacterial Proteins↗
PubMedDate not supplied

Dietary zinc oxide in weaned pigs--effects on performance, tissue concentrations, morphology, neutrophil functions and faecal microflora.

The uptake and distribution of zinc in tissues and the effects of 2500 ppm dietary zinc oxide on health, faecal microflora, and the functions of circulating neutrophils were evaluated in weaned pigs. One group was fed a zinc supplement diet and another group was used as a control. All pigs remained healthy throughout the study, but the supplemented animals showed better performance than the controls. The serum zinc values rose rapidly. At autopsy, carried out at the age of 63 days, the zinc concentrations in liver tissue were 4.5 times higher, and in renal tissue two times higher in the supplemented group than in controls (P<0.001). Microscopic examination showed increased lipid accumulation in hepatocytes from supplemented pigs. No effect on the number of excreted Escherichia coli and enterococci per gram faeces or on the functions of circulating neutrophils was observed. Dietary supplementation with 2500 ppm ZnO for up to two weeks after weaning appears to be potentially beneficial in the prevention of postweaning diarrhoea in pigs.

Animal Feed↗
PubMedDate not supplied

Reversal of primary root caries using dentifrices containing 5,000 and 1,100 ppm fluoride.

This study compared the ability of two sodium fluoride dentifrices, one containing 5,000 ppm fluoride (Prevident 5000 Plus) and the other 1,100 ppm fluoride (Winterfresh Gel), to reverse primary root caries lesions (PRCLs). A total of 201 subjects with at least one PRCL each entered the study and were randomly allocated to use one of the dentifrices. After 6 months, 186 subjects were included in statistical analyses. At baseline and after 3 and 6 months, the lesions were clinically assessed and their electrical resistance measured using an electrical caries monitor. After 3 months, 39 (38.2%) of the 102 subjects in the 5,000 ppm F- group and 9 (10.7%) of 84 subjects using the 1,100 ppm F- dentifrice, had one or more PRCLs which had hardened (p = 0.005). Between baseline and 3 months, the log10 mean +/- SD resistance values of lesions for subjects in the 1,100 ppm F- group had decreased by 0.06+/-0.55, whereas those in the 5,000 ppm F- group had increased by 0.40+/-0.64 (p<0.001). After 6 months, 58 (56.9%) of the subjects in the 5,000 ppm F- group and 24 (28.6%) in the 1,100 ppm F- group had one or more PRCLs that had become hard (p = 0.002). Between baseline and 6 months, the log10 mean +/- SD resistance values of lesions for subjects in the 1,100 ppm F- group decreased by 0.004+/-0.70, whereas in the 5,000 ppm F- group, they increased by 0.56+/-0.76 (p<0.001). After 3 and 6 months, the distance from the apical border of the root caries lesions to the gingival margin increased significantly in the 5,000 ppm F- group when compared with the 1,100 ppm F- group. The plaque index in the 5,000 ppm F- group was also significantly reduced when compared with the 1,100 ppm F- group. The colour of the lesions remained unchanged. It was concluded that the dentifrice containing 5,000 ppm F- was significantly better at remineralising PRCLs than the one containing 1,100 ppm F-.

Adult↗