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Biomedical subjects

K Johnsson

Publications and source records attributed to K Johnsson.

At least 19 recordsLinked to original sources
PubMed2004

A combined RSA and FE study of the implanted proximal tibia: correlation of the post-operative mechanical environment with implant migration.

There is strong evidence to suggest that inducible displacements, migration and implant loosening are closely related to the initial mechanical environment of the implanted tibia. If this is true, then it should be possible to predict the likelihood of implant migration using patient-specific finite element models. Finite element models of the proximal implanted tibiae were analysed based on pre-operative quantitative computed tomography data of four patients entered into a radiographic migration study. These four patients were also part of an radiostereometric analysis (RSA) study. A variety of load cases were analysed and the risk of bone failure determined for a 2 mm layer of bone immediately beneath the tibial tray. The results were compared with the RSA data measured 1 year post-operatively for each patient. For each patient, an appropriate load case was selected based on patient weight and on the varus-valgus migrations observed in the migration study. The two patients with press-fit implants were predicted to have the highest risk of failure and were found to migrate the most. The two patients with bonded implants (one HA coated and one cemented) were found to have a low risk of failure and these implants migrated the least. This study suggests that the degree of implant migration is dependent on the initial mechanical environment and can be determined using patient-specific finite element analysis.

Aged↗
PubMed2001

Inter- and intramolecular domain interactions of the catalase-peroxidase KatG from M. tuberculosis.

The inter- and intramolecular interactions between the different domains of the catalase-peroxidase KatG from Mycobacterium tuberculosis were analyzed using the two-hybrid assay. It was shown that the dimerization of the enzyme is due to a strong interaction of the first 99 amino acids of the N-terminal domain whereas the C-terminal domain does not play a role in the dimerization. In addition, an intramolecular interaction between the N- and C-terminal domains was detected which might play a functional role in the mechanism of the enzyme.

Amino Acid Sequence↗
PubMed2001

Changing the substrate specificity of cytochrome c peroxidase using directed evolution.

Cytochrome c peroxidase (CCP) from Saccharomyces cerevisiae was subjected to directed molecular evolution to generate mutants with increased activity against 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Using a combination of DNA shuffling and saturation mutagenesis, mutants were isolated which possessed more than 20-fold increased activity against ABTS and a 70-fold increased specificity toward ABTS compared to the natural substrate. In contrast, activities against another small organic molecule, guaiacol, were not significantly affected. Mutations at residues Asp224 and Asp217 were responsible for this increase in activity. These two residues are located on the surface of the protein and not in the direct vicinity of the distal cavity of the peroxidase, where small organic substrates are believed to be oxidized. Mutations at position Asp224 also lead to an increased amount of the active holoenzyme expressed in Escherichia coli, favoring the selection of these mutants in the employed colony screen. Possible explanations for the effect of the mutations on the in vitro activity of CCP as well as the increased amount of holoenzyme are discussed.

Base Sequence↗
PubMed2000

Directed molecular evolution of cytochrome c peroxidase.

Cytochrome c peroxidase (CCP) from Saccharomyces cerevisiae was subjected to directed molecular evolution to generate mutants with increased activity against the classical peroxidase substrate guaiacol, thus changing the substrate specificity of CCP from the protein cytochrome c to a small organic molecule. After three rounds of DNA shuffling and screening, mutants were isolated which possessed a 300-fold increased activity against guaiacol and an up to 1000-fold increased specificity for this substrate relative to that for the natural substrate. In all of the selected mutants, the distal arginine (Arg48), which is fully conserved in the superfamily of peroxidases, was mutated to histidine, showing that this mutation plays a key role in the significant increase in activity against phenolic substrates. The results suggest that, in addition to stabilizing the reactive intermediate compound I, the distal arginine plays an important role as a gatekeeper in the active site of CCP, controlling the access to the ferryl oxygen and the distal histidine. Other isolated mutations increase the general reactivity of the peroxidase or increase the intracellular concentration of the active holo form, allowing their selection under the employed screening conditions. The results illustrate the ability of directed molecular evolution technologies to deliver solutions to biochemical problems that would not be readily predicted by rational design.

Alanine↗
PubMed1999

Use of site-directed mutagenesis to probe the structure, function and isoniazid activation of the catalase/peroxidase, KatG, from Mycobacterium tuberculosis.

A series of mutants bearing single amino acid substitutions often encountered in the catalase/peroxidase, KatG, from isoniazid-resistant isolates of Mycobacterium tuberculosis has been produced by site-directed mutagenesis. The resultant enzymes were overexpressed, purified and characterized. Replacing Cys-20 by Ser abolished disulphide-bridge formation, but did not affect either dimerization of the enzyme or catalysis. The substitution of Thr-275, which is probably involved in electron transfer from the haem, by proline resulted in a highly unstable enzyme with insignificant enzyme activities. The most commonly occurring substitution in drug-resistant clinical isolates is the replacement of Ser-315 by Thr; this lowered catalase and peroxidase activities by 50% and caused a significant decrease in the KatG-mediated inhibition of the activity of the NADH-dependent enoyl-[acyl-carrier protein] reductase, InhA, in vitro. The ability of this enzyme to produce free radicals from isoniazid was severely impaired, as judged by its loss of NitroBlue Tetrazolium reduction activity. Replacement of Leu-587 by Pro resulted in marked instability of KatG, indicating that the C-terminal domain is also important for structural and functional integrity.

Amino Acid Sequence↗
PubMed1999

Spontaneous Formation of the Bioactive Form of the Tuberculosis Drug Isoniazid.

It works even without the enzyme: The formation of the bioactive form 1 of isoniazid inside Mycobacterium tuberculosis does not depend on specific interactions within the active site of the inhibited enzyme, but rather relies on the fast addition of acyl radicals to electron-deficient heterocycles such as NAD(+).

Journal Article↗
PubMed1997

Overexpression, purification, and characterization of the catalase-peroxidase KatG from Mycobacterium tuberculosis.

Wild-type catalase-peroxidase KatG from Mycobacterium tuberculosis as well as a specific mutant (R463L) frequently found in isoniazid-resistant strains have been overexpressed in Escherichia coli, allowing purification of sufficient quantities of enzyme for physical and kinetic characterization. Optical absorption and EPR spectroscopies indicate that KatG is similar to a growing class of bacterial catalase-peroxidases. Optical and EPR spectra of KatG in the presence of either a strong field or weak field ligand suggest that, like horseradish peroxidase and metmyoglobin, KatG is likely to have a histidine as a proximal ligand. The wild-type enzyme functions as a highly active catalase as well as a broad specificity peroxidase. Wild-type KatG and the R463L mutant of KatG exhibit identical spectroscopic and kinetic properties. Furthermore, both enzymes are equally capable of metabolizing the important antituberculosis drug isoniazid.

Bacterial Proteins↗
PubMed1995

Hip involvement in early rheumatoid arthritis.

OBJECTIVE: To study early hip involvement in rheumatoid arthritis (RA) and to evaluate the usefulness of ultrasonography in the detection of hip joint synovitis in RA. METHODS: Study I: The number of hip joint replacements was recorded in a cohort of 113 patients with RA of at least five years disease duration followed from an early stage. Study II: Ultrasonography was evaluated as a method to identify hip joint synovitis in 76 patients with RA of shorter disease duration, by relating it to radiograms and clinical findings. RESULTS: Study I: Twenty one hip joint replacements were performed in 15 of the 113 patients. The median disease duration at the time of first arthroplasty was 48 (range 10-76) months; the annual incidence was approximately constant between two and six years. High disease activity at the start of the study was predictive of requirement for hip prosthesis. Study II: Hip ultrasonography was pathological in 13 of the 76 patients studied, bilaterally in nine. Hip joint synovitis could not be confirmed on clinical grounds only as seven of the patients with positive ultrasonographic findings were asymptomatic, and the remaining six patients had only mild symptoms of hip involvement. Also, six of the 63 patients with normal ultrasonography had mild symptoms. There was no difference regarding demographic, clinical, and laboratory findings in patients with and without hip synovitis. CONCLUSIONS: Early hip joint destruction giving symptoms mostly at a very late stage is frequent in RA. Ultrasonography rather than signs or symptoms could identify patients with hip joint involvement and provide a rationale for early treatment.

Adult↗
PubMed1995

Measuring hallux valgus: a comparison of conventional radiography and clinical parameters with regard to measurement accuracy.

To assess the repeatability and error of conventional x-ray measurements, intra- and interobserver evaluations of measurement accuracy were done on 20 preoperative and 40 postoperative (20 chevron and 20 proximal osteotomy) x-rays of hallux valgus patients. Standard x-rays showed an average interobserver error of measurement of 6.4 degrees for the hallux valgus angle, 5.4 degrees for the intermetatarsal angle, and 2.0 mm for the intermetatarsal distance. The intraobserver error did not differ greatly. The repeatability and error of two clinical measurements, ball circumference, and dorsal to plantar range of motion of the first metatarsophalangeal joint were evaluated for 20 healthy volunteers. The ball circumference had an average measurement error of 1.1 cm, whereas the dorsal and plantar range of motion of the great toe had an average measurement error of 12 degrees in dorsiflexion and 16 degrees in plantarflexion. In both clinical and radiographic parameters, linear measurements were more accurate than angular measurements. Although x-rays are of value in hallux valgus surgery, standard x-rays are less accurate than previously assumed. Small changes produced by osteotomies may be hidden by the postoperative measurement error. The results of hallux valgus surgery should primarily be evaluated clinically. When clinical and radiological evaluations are made, linear measurements may be preferable.

Female↗
PubMed1993

Synthesis, structure and activity of artificial, rationally designed catalytic polypeptides.

Biological macromolecules with catalytic activity can be created artificially using two approaches. The first exploits a system that selects a few catalytically active biomolecules from a large pool of randomly generated (and largely inactive) molecules. Catalytic antibodies and many catalytic RNA molecules are obtained in this way. The second involves rational design of a biomolecule that folds in solution to present to the substrate an array of catalytic functional groups. Here we report the synthesis of rationally designed polypeptides that catalyse the decarboxylation of oxaloacetate via an imine intermediate. We determine the secondary structures of the polypeptides by two-dimensional NMR spectroscopy. We are able to trap and identify intermediates in the catalytic cycle, and to explore the kinetics in detail. The formation of the imine by our artificial oxaloacetate decarboxylases is three to four orders of magnitude faster than can be achieved with simple amine catalysts: this performance rivals that of typical catalytic antibodies.

Amines↗
PubMed1993

The effects of hyperbaric oxygenation on bone-titanium implant interface strength with and without preceding irradiation.

This study investigated the influence of a single 15-Gy dose of irradiation on the capacity of titanium screws to integrate in irradiated bone tissue. The biomechanical force necessary to unscrew the titanium implants 8 weeks after placement was 54% lower for implants in irradiated bone tissue compared to implants in nonirradiated bone tissue. Postirradiation use of hyperbaric oxygen treatment at 2.8 ATA (2-hour daily treatments for 21 days) increased the biomechanical force necessary to unscrew the titanium implants by 44% in irradiated bone and by 22% in nonirradiated bone.

Animals↗
PubMed1991

Comparison of iopromide versus iohexol in aortobifemoral arteriography. A Swedish multi-center study of 446 patients.

A double-blind randomized, clinical trial was conducted in 9 hospitals comparing the use of non-ionic contrast media (CM) iopromide 300 (Ultravist) and iohexol 300 (Omnipaque) during peripheral arteriography in a total of 446 patients. After premedication with morphine-scopolamine each patient was given two consecutive injections of 50 ml CM at a rate of 12 ml/s above the aortic bifurcation. Both CM were well tolerated. There were no differences between the two substances as far as general tolerance, pulse rate, blood pressure, sensation of heat or pain after CM injection were concerned.

Adult↗
PubMed1990

Staff interaction with vocally disruptive demented patients compared with demented controls.

This study addressed the effect of social isolation on vocally disruptive demented patients (V); the results center on the amount of time patients spent in interactions, and the differences in type and time of staff-patient interaction (IA), compared to controls (C). Semi-structured observations were collected (1100 hours) for 37 vocally disruptive patients and 37 controls, all residents of psychogeriatric wards. Quantitative analysis revealed a low frequency of interactions, elicited mainly for procedural matters and short duration of most interaction episodes. Multiple regression analysis showed a significant difference in the type of interaction: there was more correction of undesired behaviour for vocally disruptive patients than for controls. The results show that social isolation is part of the institutionalized demented patients' life. The dominance of short interaction episodes could contribute to overstimulation. The only significant difference found was the frequency of corrective interactions in the group of vocally disruptive patients. We conclude that this is not the cause of their behaviour, but it may reinforce it. Other factors that might cause and maintain this behaviour require investigation.

Aged↗
PubMed1988

A discontinuous epitope on p36, the major substrate of src tyrosine-protein-kinase, brings the phosphorylation site into the neighbourhood of a consensus sequence for Ca2+/lipid-binding proteins.

Previous models of p36 based on proteolytic fragments describe the tail and core as two noninteracting domains. However, the monoclonal antibody H28 recognizes a discontinuous epitope, which covers the peptide segments around Ser 25 in the tail and around Glu 65 in the core of porcine p36. Thus, the phosphorylatable Tyr 23 is much closer to the first consensus sequence (residues 46-62) of Ca2+/lipid-binding proteins than previously thought. This apposition is in line with biochemical experiments indicating an influence of core ligands on tyrosine phosphorylation and an enhanced Ca2+ requirement of the modified p36 in phospholipid binding.

Amino Acid Sequence↗
PubMed1988

Fate of bone grafts in acetabular roof reconstructions assessed by roentgenography and scintigraphy.

Autogeneic bone grafts--26 femoral heads, four femoral and two iliac bone grafts--were used in 32 total hip arthroplasties, mainly on patients with complete dislocation of the hip, to reconstruct deficiencies of the acetabular roof by a standardized procedure. At the follow-up examination after 24 to 101 months (median, 52 months), roentgenography demonstrated lateral resorption of the graft in 20 of 32 hips, but resorption involved bone support of the socket in only three of the hips. Analysis of serial roentgenograms showed that resorption was not a function of time. Complete incorporation of the grafts was observed in 27 hips; partial incorporation was shown in three. Roentgenographically, two grafts were not incorporated. None of three grafts of a cortical nature was incorporated. Graft uptake of radioactive tracer was found by 99mTc-diphosphonate emission scintigraphy in 16 of 21 hips, but did not correlate with progressive bone resorption, nonunion, or loss of bone structure. High quality serial roentgenograms showing good bone detail provided the best information about the integrity of the acetabular roof reconstructions.

Acetabulum↗