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Biomedical subjects

M Wikström

Publications and source records attributed to M Wikström.

At least 127 records · Page 7Linked to original sources
PubMed1994

The histidine cycle: a new model for proton translocation in the respiratory heme-copper oxidases.

A model of redox-linked proton translocation is presented for the terminal heme-copper oxidases. The new model, which is distinct both in principle and in detail from previously suggested mechanisms, is introduced in a historical perspective and outlined first as a set of general principles, and then as a more detailed chemical mechanism, adapted to what is known about the chemistry of dioxygen reduction in this family of enzymes. The model postulates a direct mechanistic role in proton-pumping of the oxygenous ligand on the iron in the binuclear heme-copper site through an electrostatic nonbonding interaction between this ligand and the doubly protonated imidazolium group of a conserved histidine residue nearby. In the model this histidine residue cycles between imidazolium and imidazolate states translocating two protons per event, the imidazolate state stabilized by bonding to the copper in the site. The model also suggests a key role in proton translocation for those protons that are taken up in reduction of O2 to water, in that their uptake to the oxygenous ligand unlatches the electrostatically stabilized imidazolium residue and promotes proton release.

Animals↗
PubMed1994

Measurement of magnetic susceptibility and MR contrast agent concentration.

This paper describes an MR imaging method for determining magnetic susceptibility constants of solutions containing paramagnetic contrast agents. The method's validity is demonstrated on Gd(DTPA) and Dy(DTPA) water solutions. The method can be used for measurement of the volume magnetic susceptibility or concentration of contrast agents in biological tissues.

Animals↗
PubMed1994

Detection of Porphyromonas gingivalis in gingival exudate by a dipeptide-enhanced trypsin-like activity.

Porphyromonas gingivalis in subgingival plaque is an important risk factor for future periodontal attachment loss in susceptible adults. The elimination of P. gingivalis is usually concomitant with a healing process. Therefore, it should be valuable to have an easy chairside method to follow the effect of periodontal treatment on P. gingivalis detection as well as on its eventual reappearance during the maintenance period. We have previously reported the stimulation of amidolytic activity of P. gingivalis by the addition of glycyl-glycine to the assay buffer. In this study we determined the proportions of P. gingivalis, Prevotella intermedia, Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum, Capnocytophaga spp, Campylobacter rectus, and Eikenella corrodens by cultivation technique and the amidolytic activity, using N-benzoyl-L-arginine-p-nitroanilide (BAPNA) as substrate, in gingival exudate before and during a 3-year treatment and maintenance period. P. gingivalis was the only species yielding a high and persistent correlation to stimulated amidolytic activity (P values < or = 0.0001) on both site (r = 0.5) and subject (r = 0.8) level. Testing pure cultures of suggested periodontal pathogens for effect of glycyl-glycine on amidolytic activity, we found that of P. gingivalis to be 5.9-fold increased. The amidolytic activity of Treponema denticola was only slightly stimulated (ratio with/without glycyl-glycine = 1.2) and that of Capnocytophaga slightly inhibited (ratio with/without glycyl-glycine = 0.8). The outcome of this study has the potential to be used for the development of a simple, rapid, and inexpensive assay for a qualitative and quantitative determination of P. gingivalis in gingival crevicular fluid.

Adult↗
PubMed1994

[Computerized tomography measurement of torsion angle of the lower extremities].

The precise evaluation of post-traumatic deformities is indispensable when planning a corrective osteotomy. Torsional angles of the lower extremities of 186 patients were measured using CT. The mean age of the studied population was 34 years (18-80). It consisted of 131 men and 55 women. All patients had sustained a fracture of at least one of the leg's bony segments. The normal femoral (n = 293) inward torsion measured 23.47 degrees +/- 17.16 degrees (mean +/- 2 SD). Normal tibia (n = 263) outward torsion was 34.03 degrees +/- 17.22 degrees. The intraindividual torsional differences were not normally distributed. Normal femoral (n = 103) intraindividual torsional difference measured 11 degrees (95% percentile) and 15 degrees (99% percentile), with a median of 4 degrees. The tibiae (n = 76) showed a normal intraindividual torsional difference of 12 degrees (95% percentile) and 15 degrees (99% percentile). Right tibiae showed a statistically significant greater outward rotation when compared to their left counterpart (P < 0.001). No correlation to sex could be established. Preoperative planning of a corrective osteotomy should include the geometric evaluation of all four bony segments of the leg. Intraindividual torsional differences must be considered. A corrective osteotomy appears to be unnecessary with a torsional difference smaller than 15 degrees in the femora and smaller than 15 degrees in the tibiae.

Adolescent↗
PubMed1993

Intramolecular electron transfer in cytochrome o of Escherichia coli: events following the photolysis of fully and partially reduced CO-bound forms of the bo3 and oo3 enzymes.

The events which follow photolysis of CO-inhibited fully reduced and CO-bound mixed-valence cytochrome o have been studied in two variants of the enzyme, one of which contains heme B at the low-spin site (bo3) and the other of which contains heme O (oo3). For this, isolated enzyme was prepared from three different strains of Escherichia coli which produce these two variants in different relative amounts [Puustinen, A., Morgan, J. E., Verkhovsky, M., Thomas, J. W., Gennis, R. B., & Wikström, M. (1992) Biochemistry 31, 10363-10369]. In both types of enzyme microsecond electron redistribution was observed from the oxygen-binding heme to the low-spin heme. In the bo3 enzyme, the rate was similar to that in the bovine enzyme (3 microseconds), but in the oo3 enzyme, it was several times slower. However, in both types of cytochrome o, the same electron redistribution process was also apparently observed on other time scales, some faster and some slower. The rate of CO rebinding in the mixed-valence enzyme was found to be slower than in the fully reduced enzyme, apparently because of the subpopulation of oxidized oxygen-binding heme produced by the electron redistribution. The extent of this electron redistribution, and thus the inter-heme delta Em, can be calculated from this change in rate. The heme B and heme O containing low-spin sites have Em values about 20 and 50 mV lower, respectively, than the oxygen-binding heme.

Carbon Monoxide↗
PubMed1993

Substitution of asparagine for aspartate-135 in subunit I of the cytochrome bo ubiquinol oxidase of Escherichia coli eliminates proton-pumping activity.

The terminal quinol oxidase, cytochrome bo, of Escherichia coli is a member of the large terminal oxidase family, which includes cytochrome aa3-type terminal oxidases from bacteria, plants, and animals. These enzymes conserve energy by linking electron transfer to vectorial proton translocation across mitochondrial or bacterial cell membranes. Site-directed mutagenesis of the five most highly conserved acidic amino acids in subunit I of cytochrome bo was performed to study their role in proton transfer. Mutation of only one of these sites, Asp135, to the corresponding amide, results in a dramatic decrease in proton pumping but with little change in electron-transfer activity. However, the conservative mutation Asp135Glu is active in proton translocation. It is proposed that an acidic residue at position 135 in subunit I may be important to form a functional proton input channel of the proton pump.

Amino Acid Sequence↗
PubMed1993

The cis/trans interconversion of the calcium regulating hormone calcitonin is catalyzed by cyclophilin.

The cytosolic peptidyl-prolyl cis/trans isomerase cyclophilin from pig kidney can accelerate catalytically the cis/trans isomerization of prolyl peptide bonds. One- and two-dimensional 1H NMR spectroscopy was used to prove that the polypeptide hormone calcitonin is a substrate for cyclophilin. Isomerization of only one of the two prolyl peptide bonds is catalyzed significantly. The efficiency of catalysis was calculated by lineshape analysis and NOESY spectroscopy. Cyclosporin A completely blocks the effect of the enzyme on the conformational dynamics of the polypeptide.

Amino Acid Isomerases↗
PubMed1993

The terminal quinol oxidases of Bacillus subtilis have different energy conservation properties.

We have analyzed the respiratory chains in the log-arithmic and stationary growth phases of Bacillus subtilis cells grown in rich glucose medium. The cytochrome c branch of the respiratory chain was absent from both types of cells, which used a quinol oxidase branch for respiration. Cytochrome aa3-600 was found to be the major terminal oxidase in log phase cells. This enzyme was shown to translocate protons across the membrane in addition to the charge separation in the oxidation of quinol. Both cytochromes d and aa3-600 were expressed in the stationary phase. After inhibition of the latter by cyanide, cytochrome d was shown to catalyze charge separation during quinol oxidation, but not to pump protons across the membrane. A CO-binding membrane-bound cytochrome of approximately 17 kDa, called cytochrome b558, was presented in log phase cells. This protein did not exhibit oxidase activity and did not have the characteristics of members of the conserved terminal oxidase family.

Bacillus subtilis↗
PubMed1993

Proton nuclear magnetic resonance sequential assignments and secondary structure of an immunoglobulin light chain-binding domain of protein L.

The 1H NMR assignments have been made for the immunoglobulin (Ig) light chain-binding B1 domain of protein L from Peptostreptococcus magnus. The secondary structure elements and the global folding pattern were determined from nuclear Overhauser effects, backbone coupling constants, and slowly exchanging amide protons. The B1 domain was found to be folded into a globular unit of 61 amino acid residues, preceded by a 15 amino acid long disordered N-terminus. The folded portion of the molecule contains a four-stranded beta-sheet spanned by a central alpha-helix. The fold is similar to the IgG-binding domains of streptococcal protein G, despite the fact that the binding sites on immunoglobulins for the two proteins are different; protein G binds IgG through the constant (Fc) part of the heavy chain, whereas protein L has affinity for the variable domain of Ig light chains.

Amino Acid Sequence↗
PubMed1993

Peroxy and ferryl intermediates of the quinol-oxidizing cytochrome aa3 from Bacillus subtilis.

The quinol-oxidizing cytochrome aa3-600 from Bacillus subtilis has a binuclear heme a3-CuB center of O2 reduction and a low-spin heme a, but lacks a fourth redox center, CuA, which is a typical component of cytochrome c oxidases. Fully reduced (3e-) cytochrome aa3-600 and the two-electron-reduced CO complex were allowed to react with O2 at 0 degree C, and the reaction products were studied by optical spectroscopy. When the two-electron-reduced CO complex (heme a3 and CuB are reduced, but the low-spin heme is oxidized) reacts with O2 at neutral pH, a compound is produced that may be assigned a ferric-cupric peroxy structure (P). At low pH, this species spontaneously decomposes into another compound, which may be assigned a ferryl structure (F). When fully reduced enzyme (3e-) reacts with O2 at high pH, a peroxy species is the primary product. This subsequently decays into F, followed by very slow decay of the latter. Our data show that at high pH the third electron, which is required to convert P into F, resides for a relatively long time in either CuB or heme a3. This suggests that transfer of the third electron to the binuclear center is followed by proton uptake, which must occur before scission of the O-O bond. The present data strongly support the involvement of discrete peroxy and ferryl intermediates in the catalytic cycle of cytochrome aa3-600. The dioxygen reduction mechanism in the binuclear site is thus very similar in the quinol and the cytochrome c oxidases.

Bacillus subtilis↗
PubMed1993

A longitudinal microbiological study on osseointegrated titanium implants in partially edentulous patients.

The aim was to longitudinally follow the colonization of putative periodontal pathogens on titanium implants in partially edentulous patients. Nineteen individuals, who were partially edentulous and were on the waiting-list to be treated with titanium fixtures, were included in the study. They were treated for periodontal disease with oral hygiene instructions and supra- and subgingival debridement and were left for maintenance. Full-mouth recordings of each patient were performed at baseline, including attachment level and probing pocket depth. Bleeding was provoked and visible plaque were registered. Subgingival samples were taken for examination of Porphyromonas gingivalis, Prevotella intermedia and Actinobacillus actinomycetemcomitans. Bridge connection was completed 1 month after abutment connection. The bone level was registered on radiographs. The patients were followed with clinical registrations and subgingival samples at 6, 12, 24 and 36 months. No significant changes in pocket depth, attachment level, bleeding on probing or plaque score occurred during the experimental period. The number of individuals positive at teeth and abutments for the various bacterial species reached approximately similar levels at 6 months. No significant changes over time were seen. Comparison between bone height, seen on radiographs, at abutments after 2, 12 and 36 months gave only 3 sites with bone loss of > 0.5 mm. All these sites were found in one patient and were accompanied by P. intermedia.

Adult↗
PubMed1993

Microbial associations in periodontitis sites before and after treatment.

Duplicate samples from 110 periodontal sites of 6 mm or more pocket depth in 16 patients were analyzed for the presence of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Capnocytophaga spp., Campylobacter rectus, Eikenella corrodens and Fusobacterium nucleatum. The sites were sampled before and after nonsurgical periodontal treatment. No statistically significant associations were found before treatment between any of the analyzed species. After treatment, statistically significant associations were found between E. corrodens and all the other species, F. nucleatum and P. intermedia; Capnocytophaga spp. and C. rectus; P. intermedia vs Capnocytophaga spp. and P. gingivalis; and C. rectus vs Capnocytophaga spp. and A. actinomycetemcomitans. Some of these associations could be explained either by patient-related factors or site-related characteristics such as the pocket depth. The proportion of P. gingivalis seemed to be unrelated to the proportion of P. intermedia in the samples. If one of the analyzed microbes was found in one of the sampled pockets in a patient, the probability of finding that microbe in all the sampled sites in the same patient before treatment was more than 50%. This probability was reduced after treatment for many species, especially P. gingivalis, which showed a probability of zero. The probability of detecting a bacterial species on at least one additional site if it was present on one in the same individual was nearly 100%, both before and after treatment, for all species studied. This study has shown several potential microbial associations in the subgingival plaque flora of deep periodontal pockets.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Double-contrast enhanced MR imaging of myocardial infarction in the pig.

Myocardial infarction was induced by ligating a diagonal branch of the left anterior descending artery in 18 pigs. All pigs were sacrificed 6 h after the occlusion. Dysprosium diethylenetriamine-pentaacetic acid bismethylamide (Dy-DTPA-BMA, 1.0 mmol/kg) was administered i.v. to 6 pigs, starting 3 min before sacrifice (injection time approximately 1 min). In a second group of 6 pigs, a double-contrast technique was used, consisting of an i.v. injection of gadolinium-DTPA-BMA (0.4 mmol/kg) 2 h before sacrifice, followed by an i.v. injection of Dy-DTPA-BMA (1.0 mmol/kg) 3 min before sacrifice. Six additional pigs, subjected to 6 h of coronary artery occlusion without administration of contrast medium, served as controls. The hearts were excised and imaged with MR. In the control animals, the infarctions demonstrated an increased signal intensity in the proton density- and T2-weighted images. Administration of Dy-DTPA-BMA primarily improved infarct visualization in the proton density- and T2-weighted images, due to reduction of signal intensity in nonischemic myocardium. The double-contrast technique further improved infarct visualization in all sequences.

Animals↗
PubMed1992

Intramolecular electron transfer in cytochrome c oxidase: a cascade of equilibria.

Intramolecular electron redistribution in cytochrome c oxidase after photolysis of the partially reduced CO-bound enzyme was followed at a number of different wavelengths by absorption spectroscopy. Spectra were constructed for the first two phases of this process. The first phase (tau = 3 microseconds) has a spectrum essentially identical to the difference between the Fea and Fea3 reduced-minus-oxidized spectra, indicating a 1:1 stoichiometry between the amount of Fea3 oxidized and Fea reduced. It is not necessary to invoke reduction or oxidation of other redox carriers in this phase. The second phase (tau = 35 microseconds) spectrum appears to be a linear combination of the Fea3 and Fea reduced-minus-oxidized difference spectra, reflecting the oxidation of four parts of Fea3 for every part of Fea oxidized. This process can be described in terms of transfer to CuA of electrons from the Fea3<==>Fea equilibrium system established in the first phase. The relative contributions of Fea3 and Fea in the second phase allow us to calculate the equilibrium constant for Fea3<==>Fea electron exchange, which yields a delta Em of 36 mV for the two centers (Fea3 more positive). Together with the apparent rate constant for the fast phase, this equilibrium constant yields, in turn, the forward (kf) and reverse (kr) rates for electron transfer from Fea to Fea3 as follows: kf = 2.4 x 10(5) s-1 and kr = 6 x 10(4) s-1. kf is much faster than any observed step in the reaction of the reduced enzyme with O2. Thus, the catalytic mechanism of O2 reduction to water is not rate-limited by electron transfer from Fea to the binuclear Fea3/Cu(B) site.

Animals↗
PubMed1992

The low-spin heme site of cytochrome o from Escherichia coli is promiscuous with respect to heme type.

Cytochrome o of Escherichia coli is able to incorporate two different structures of heme, either heme B (protoheme) or heme O, in its low-spin heme site. In contrast, the heme of the binuclear O2 reduction site is invariably heme O. Heme O is a newly discovered heme that is related to heme A, but with the formyl group of the latter replaced by methyl. Enzyme isolated from wild type E. coli has predominantly heme B in the low-spin site, whereas enzyme isolated from various overexpressing strains contains both types of enzyme in different proportions. In some strains, 70% of the enzyme has heme O in the low-spin site. Despite this variation in the structure of one of the prosthetic groups, the enzymatic activity and polypeptide composition of the enzyme remain virtually constant. EPR and activity data both indicate that heme B and heme O occupy the same low-spin heme site in the enzyme. With heme O in this site, the alpha-absorption band is narrower and further to the blue, and the Em,7 is lower, than when there is heme B in the site. In contrast to previous proposals, we show here that the enzyme does not exhibit significant spectral interactions between the hemes. The structural heterogeneity of the low-spin heme accounts for the variation in the optical spectra and redox properties of the enzyme as isolated from different strains of E. coli.

Binding Sites↗
PubMed1992

Optical and resonance Raman spectroscopy of the heme groups of the quinol-oxidizing cytochrome aa3 of Bacillus subtilis.

The cytochrome aa3-type terminal quinol oxidase of Bacillus subtilis catalyzes the four-electron reduction of dioxygen to water. It resembles the aa3-type cytochrome-c oxidase in using heme A as its active-site chromophores but lacks the CuA center and the cytochrome-c oxidizing activity of the mitochondrial enzyme. We have used optical and resonance Raman spectroscopies to study the B. subtilis oxidase in detail. The alpha-band absorption maximum of the reduced minus oxidized enzyme is shifted by 5-7 nm to the blue relative to most other aa3-type oxidases, and accordingly, we designate the Bacillus enzyme as cytochrome aa3-600. The shifted optical spectrum cannot be ascribed to an alteration in the strength of the hydrogen bond between the formyl group of the low-spin heme and its environment, as the Raman line assigned to this mode in aa3-600 has the same frequency and degree of resonance enhancement as the low-spin heme a formyl mode in most other aa3-type oxidases. Raman modes arise at 194 and 214 cm-1 in aa3-600, whereas a single band at about 214 cm-1 is assigned to the iron-histidine stretch for the other aa3-type oxidases. Possible explanations for the occurrence of these two modes are discussed. Comparison of formyl and vinyl modes and heme skeletal vibrational modes in different oxidation states of aa3-600 and of beef heart cytochrome-c oxidase shows a strong similarity, which suggests conservation of essential features of the heme environments in these oxidases.

Bacillus subtilis↗
PubMed1992

Convergent evolution among immunoglobulin G-binding bacterial proteins.

Protein G, a bacterial cell-wall protein with high affinity for the constant region of IgG (IgGFc) antibodies, contains homologous repeats responsible for the interaction with IgGFc. A synthetic peptide corresponding to an 11-amino acid-long sequence in the COOH-terminal region of the repeats was found to bind to IgGFc and block the interaction with protein G. Moreover, two other IgGFc-binding bacterial proteins (proteins A and H), which do not contain any sequences homologous to the peptide, were also inhibited in their interactions with IgGFc by the peptide. Finally, a decapeptide based on a sequence in IgGFc blocked the binding of all three proteins to IgGFc. This unusually clear example of convergent evolution emphasizes the complexity of protein-protein interactions and suggests that bacterial surface-protein interaction with host protein adds selective advantages to the microorganism.

Amino Acid Sequence↗