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Biomedical subjects

A S Johansson

Publications and source records attributed to A S Johansson.

At least 19 recordsLinked to original sources
PubMed2001

Human glutathione transferase A3-3, a highly efficient catalyst of double-bond isomerization in the biosynthetic pathway of steroid hormones.

The cDNA of a novel human glutathione transferase (GST) of the Alpha class was cloned, and the corresponding protein, denoted GST A3-3, was heterologously expressed and characterized. GST A3-3 was found to efficiently catalyze obligatory double-bond isomerizations of Delta(5)-androstene-3,17-dione and Delta(5)-pregnene-3,20-dione, precursors to testosterone and progesterone, respectively, in steroid hormone biosynthesis. The catalytic efficiency (k(cat)/K(m)) with Delta(5)-androstene-3,17-dione was determined as 5 x 10(6) m(-1) s(-1), which is considerably higher than with any other GST substrate tested. The rate of acceleration afforded by GST A3-3 is 6 x 10(8) based on the ratio between k(cat) and the rate constant for the nonenzymatic isomerization of Delta(5)-androstene-3,17-dione. Besides being high in absolute numbers, the k(cat)/K(m) value of GST A3-3 exceeds by a factor of approximately 230 that of 3beta-hydroxysteroid dehydrogenase/isomerase, the enzyme generally considered to catalyze the Delta(5)-Delta(4) double-bond isomerization. Furthermore, GSTA3-specific polymerase chain reaction analysis of cDNA libraries from various tissues showed a message only in those characterized by active steroid hormone biosynthesis, indicating a selective expression of GST A3-3 in these tissues. Based on this finding and the high activity with steroid substrates, we propose that GST A3-3 has evolved to catalyze isomerization reactions that contribute to the biosynthesis of steroid hormones.

Amino Acid Sequence↗
PubMed2000

Glutathione transferase M2-2 catalyzes conjugation of dopamine and dopa o-quinones.

Human glutathione transferase M2-2 prevents the formation of neurotoxic aminochrome and dopachrome by catalyzing the conjugation of dopamine and dopa o-quinone with glutathione. NMR analysis of dopamine and dopa o-quinone-glutathione conjugates revealed that the addition of glutathione was at C-5 to form 5-S-glutathionyl-dopamine and 5-S-glutathionyl-dopa, respectively. Both conjugates were found to be resistant to oxidation by biological oxidizing agents such as O(2), H(2)O(2), and O(*-)(2), and the glutathione transferase-catalyzed reaction can therefore serve a neuroprotective antioxidant function.

Benzoquinones↗
PubMed2000

The human glutathione transferase P1-1 specific inhibitor TER 117 designed for overcoming cytostatic-drug resistance is also a strong inhibitor of glyoxalase I.

gamma-L-Glutamyl-S-(benzyl)-L-cysteinyl-R-(-)-phenylglycine (TER 117) has previously been developed for selective inhibition of human glutathione S-transferase P1-1 (GST P1-1) based on the postulated contribution of this isoenzyme to the development of drug resistance in cancer cells. In the present investigation, the inhibitory effect of TER 117 on the human glyoxalase system was studied. Although designed as an inhibitor specific for GST P1-1, TER 117 also competitively inhibits glyoxalase I (K(I) = 0.56 microM). In contrast, no inhibition of glyoxalase II was detected. Reduced glyoxalase activity is expected to raise intracellular levels of toxic 2-oxoaldehydes otherwise eliminated by glyoxalase I. The resulting toxicity would accompany the potentiation of cytostatic drugs, caused by inhibition of the detoxication effected by GST P1-1. TER 117 was designed for efficient inhibition of the most abundant form GST P1-1/Ile105. Therefore, the inhibitory effect of TER 117 on a second allelic variant GST P1-1/Val105 was also studied. TER 117 was shown to competitively inhibit both GST P1-1 variants. The apparent K(I) values at glutathione concentrations relevant to the intracellular milieu were in the micromolar range for both enzyme forms. Extrapolation to free enzyme produced K(I) values of approximately 0.1 microM for both isoenzymes, reflecting the high affinity of GST P1-1 for the inhibitor. Thus, the allelic variation in position 105 of GST P1-1 does not affect the inhibitory potency of TER 117. The inhibitory effects of TER 117 on GST P1-1 and glyoxalase I activities may act in synergy in the cell and improve the effectiveness of chemotherapy.

Drug Resistance, Neoplasm↗
PubMed1999

Use of silent mutations in cDNA encoding human glutathione transferase M2-2 for optimized expression in Escherichia coli.

Heterologous expression of human glutathione transferase M2-2 (GST M2-2) using Escherichia coli was improved 140-fold by mutating the cDNA expressing the enzyme. Expression of GST M2-2 from this cDNA clone, pKHXhGM2, generated approximately 190 mg protein per liter of bacterial culture, corresponding to approximately 12% of the total amount of soluble protein. The high-level-expressing cDNA was generated by oligonucleotide-directed mutagenesis introducing alternative silent mutations into the third nucleotide of codons 2, 4-7, and 10-14 in the 5' end of the cDNA coding region. The choice of alternative codons was restricted to those naturally occurring in highly biased genes in E. coli. Furthermore, the wild-type TAG stop codon at the 3' end was replaced with the two stop codons TAA and TGA in tandem to increase translation termination efficiency. The resulting partially randomized cDNA library was assayed for high-level expression using immunoscreening. Sequence similarities between the constructed high-level-expressing GST M2-2 cDNA and a similarly designed cDNA encoding the closely related human GST M1-1 suggest that the codons in the region immediately following the start codon are influential in achieving high-level expression. Pyrimidines seem to be more favorable than purines in the third position of codons in optimizing the expression of these enzymes in E. coli.

Amino Acid Sequence↗
PubMed1999

Establishment and characterization of a mouse strain (TLL) that spontaneously develops T-cell lymphomas/leukemia.

In this study, a mouse strain (TLL) that spontaneously develops T-cell lymphomas/leukemia with an early onset and high incidence was established and characterized. All tumors analyzed were found to express the alpha,beta T-cell receptor, and the majority of them had a mature, CD3+CD4+CD8- immunophenotype. In a few cases, tumors with a more immature CD3+CD4+CD8+ phenotype were isolated. Expanded phenotyping using a broad panel of lymphocyte differentiation markers confirmed the mature T-cell phenotype of the tumors. Histologic and cell cycle analysis of the tumors revealed an aggressive lymphoblastic malignancy with a very high proliferation rate and widespread engagement of bone marrow and lymphoid as well as nonlymphoid organs. Thus, the TLL mouse strain represents a unique model for the analysis of the oncogenesis and progression of mature T-cell tumors and for the development of therapeutic measures to combat such tumors.

Animals↗
PubMed1998

Structure-activity relationships and thermal stability of human glutathione transferase P1-1 governed by the H-site residue 105.

Human glutathione transferase P1-1 (GSTP1-1) is polymorphic in amino acid residue 105, positioned in the substrate binding H-site. To elucidate the role of this residue an extensive characterization of GSTP1-1/Ile105 and GSTP1-1/Val105 was performed. Mutant enzymes with altered volume and hydrophobicity of residue 105, GSTP1-1/Ala105 and GSTP1-1/Trp105, were constructed and included in the study. Steady-state kinetic parameters and specific activities were determined using a panel of electrophilic substrates, with the aim of covering different types of reaction mechanisms. Analysis of the steady-state kinetic parameters indicates that the effect of the substitution of the amino acid in position 105 is highly dependent on substrate used. When 1-chloro-2,4-dinitrobenzene was used as substrate a change in the side-chain of residue 105 seemed primarily to cause changes in the KM value, while the kcat value was not distinctively affected. With other substrates, such as 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and ethacrynic acid both kcat and KM values were altered by the substitution of amino acid 105. The constant for formation of the sigma-complex between 1,3, 5-trinitrobenzene and glutathione was shown to be dependent upon the volume of the amino acid in position 105. The nature of the amino acid in position 105 was also shown to affect the thermal stability of the enzyme at 50 degrees C, indicating an important role for this residue in the stabilization of the enzyme. The GSTP1-1/Ile105 variant was approximately two to three times more stable than the Val105 variant as judged by their half-lives. The presence of glutathione in the incubation buffer afforded a threefold increase in the half-lives of the enzymes. Thus, the thermal stability of the enzyme and depending on substrate, both KM values and turnover numbers are influenced by substitutions in position 105 of GSTP1-1.

Binding Sites↗
PubMed1998

[Late side-effects are common after treatment of Hodgkin's disease. Muscular atrophy following radiotherapy is a neglected risk].

As Hodgkin's disease (HD) is amenable to treatment, especially in the young, the majority of patients are long-term survivors and late treatment-related side-effects can become a clinical problem. After a retrospective review of the records of 134 patients treated for HD at Umeå during the period, 1975-90, and 15-50 years of age at diagnosis, a questionnaire on late side-effects of treatment was sent to the 110 survivors, of whom 90 per cent responded. Many patients reported late side-effects such as hypothyroidism, dryness of the mouth, cardiac and pulmonary problems, and fertility disorders. Of the 20 patients who reported pain and weakness of the neck and shoulders, 18 had undergone mantle field irradiation (i.e., of the lymph nodes of the neck, axillae and mediastinum). If shown to be equally effective, lower irradiation doses might be given in future, thus perhaps minimising long-term side-effects.

Adult↗
PubMed1998

Differences in the catalytic efficiencies of allelic variants of glutathione transferase P1-1 towards carcinogenic diol epoxides of polycyclic aromatic hydrocarbons.

Previous studies have identified allelic variants of the human glutathione transferase (GST) Pi gene and showed that the two different encoded proteins with isoleucine (GSTP1-1/I-105) or valine (GSTP1-1/V-105) at position 105, respectively, differ significantly in their catalytic activities with model substrates. Moreover, recent epidemiological studies have demonstrated that individuals differing in the expression of these allelic variants also differ in susceptibility to tumour formation in certain organs, including such in which polycyclic aromatic hydrocarbons (PAH) may be etiological factors. In the present study the catalytic efficiencies (kcat/Km) of these GSTP1-1 variants were determined with a number of stereoisomeric bay-region diol epoxides, known as the ultimate mutagenic and carcinogenic metabolites of PAH, including those from chrysene, benzo[a]pyrene and dibenz[a,h]anthracene. In addition, GSTP1-1 mutants in which amino residue 105 is alanine (GSTP1-1/A-105) or tryptophan (GSTP1-1/W-105) have been constructed and characterized. GSTP1-1/V-105 was found to be more active than GSTP1-1/I-105 in conjugation reactions with the bulky diol epoxides of PAH, being up to 3-fold as active towards the anti- and syn-diol epoxide enantiomers with R-absolute configuration at the benzylic oxiranyl carbon. Comparing the four enzyme variants, GSTP1-1/A-105 generally demonstrated the highest kcat/Km value and GSTP1-1/W-105 the lowest with the anti-diol epoxides. A close correlation was observed between the volume occupied by the amino acid residue at position 105 and the value of kcat/Km. With the syn-diol epoxides, such a correlation was observed with alanine, valine and isoleucine, whereas tryptophan was associated with increased kcat/Km values. The mutational replacement of isoleucine with alanine or tryptophan at position 105 did not alter the enantio selectivity of the GSTP1-1 variants compared with the naturally occurring allelic variants GSTP1-1/I-105 and GSTP1-1/V-105. Since the amino acid at position 105 forms part of the substrate binding site (H-site) the effect of increasing bulkiness is expected to cause restricted access of the diol epoxide and proper alignment of the two reactants for efficient glutathionylation. In conclusion, the present study indicates that individuals who are homozygous for the allele GSTP1* B (coding for GSTP1-1/V-105) display a higher susceptibility to malignancy because of other factors than a decreased catalytic efficiency of GSTP1-1/V-105 in the detoxication of carcinogenic diol epoxides of benzo[a]pyrene or structurally related PAH.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1997

Glutathione transferases catalyse the detoxication of oxidized metabolites (o-quinones) of catecholamines and may serve as an antioxidant system preventing degenerative cellular processes.

o-Quinones are physiological oxidation products of catecholamines that contribute to redox cycling, toxicity and apoptosis, i.e. the neurodegenerative processes underlying Parkinson's disease and schizophrenia. The present study shows that the cyclized o-quinones aminochrome, dopachrome, adrenochrome and noradrenochrome, derived from dopamine, dopa, adrenaline and noradrenaline respectively, are efficiently conjugated with glutathione in the presence of human glutathione transferase (GST) M2-2. The oxidation product of adrenaline, adrenochrome, is less active as a substrate for GST M2-2, and more efficiently conjugated by GST M1-1. Evidence for expression of GST M2-2 in substantia nigra of human brain was obtained by identification of the corresponding PCR product in a cDNA library. Glutathione conjugation of these quinones is a detoxication reaction that prevents redox cycling, thus indicating that GSTs have a cytoprotective role involving elimination of reactive chemical species originating from the oxidative metabolism of catecholamines. In particular, GST M2-2 has the capacity to provide protection relevant to the prevention of neurodegenerative diseases.

Adrenochrome↗
PubMed1991

The anterosuperior insertion of the temporomandibular joint capsule and condylar mobility in joints with and without internal derangement: a double-contrast arthrotomographic investigation.

The insertion of the anterior temporomandibular joint capsule at the temporal bone constitutes an anatomic boundary of the joint. When condylar translation exceeds this site, the joint is classified as hypermobile. In this study, the distance from the apex of the articular eminence to the antero-superior capsule insertion was assessed in double-contrast arthrotomograms from 192 joints with and without disc displacement. Maximum condylar translation was also measured. The insertion point of the antero-superior capsule was, on the average, located 4.4 mm (SD, 1.7 mm) anterior to the apex of the eminence, regardless of disc position. Hypermobility was present in 56 joints. Sixty-eight percent of the hypermobile joints had a reducing disc and 62% of all the joints with a reducing disc were hypermobile. In joints with permanent disc displacement, the condyle generally was halted posterior to the apex of the eminence, but could pass extensively anterior to it. Condylar hypermobility thus does not exclude the presence of a permanently displaced disc. In 71% of patients with hypermobility, the condition was bilateral. Because of the close topographic relationship between the joint and nerve branches in the anterior vicinity of the joint, a hypermobile condyle may mechanically irritate the masseteric and deep posterior temporal nerve branches.

Adolescent↗
PubMed1990

A radiographic and histologic study of the topographic relations in the temporomandibular joint region: implications for a nerve entrapment mechanism.

A radiographic and histologic investigation was performed in 18 temporomandibular joint (TMJ) autopsy specimens. Disc position was determined arthrotomographically. The pathway of the nerve branches in the vicinity of the joint was reconstructed from serial sagittal or frontal histologic sections. The relationship between the joint components and the different nerves running in the vicinity of the joint was studied. The results revealed the existence of topographical prerequisites for mechanical influence upon the nerve branches passing in the TMJ region. In two joints, both with a displaced disc, the auriculotemporal nerve trunk was almost in contact with the medial aspect of the condyle instead of having its normal sheltered course at the level of the condylar neck, thus exposing the nerve to the risk of mechanical irritation during condylar movements in an anteromedial direction. Two joints with normal disc position had an extension of the medial fossa wall in a caudal direction. In these joints the auriculotemporal nerve had its course between the condyle and the elongated fossa wall, exposing it to the risk of mechanical irritation during medial disc displacement. Compression of the masseteric nerve anterior to the TMJ was found in one joint with excessive condylar translation. The deep posterior temporal nerves may pass close to the anterior insertion of the joint capsule on the temporal bone, exposing them to the risk of mechanical irritation when there is condylar hypermobility. It was also found that the inferior alveolar and the lingual nerves may pass close to the medial part of the condyle. In joints with this nerve topography, a medially displaced disc could interfere mechanically with these nerves. These findings could offer an explanation for the sharp, shooting pain felt locally in the joint with jaw movements and the pain and other sensations projecting to the terminal area of distribution of the nerve branches in the vicinity of the TMJ such as the ear, temple, cheek, tongue, and teeth.

Aged↗
PubMed1986

Hyperplastic soft-tissue formation in the temporomandibular joint associated with internal derangement. A radiographic and histologic study.

Hyperplastic connective tissue formation in the posterior part of the temporomandibular joint glenoid fossa has previously been described in autopsy specimens. The frequency of such hyperplastic tissue formation in patients with long-standing temporomandibular joint pain was studied in 103 joints from 80 patients by means of double-contrast arthrotomography. Five joints in four patients (5%) demonstrated hyperplastic tissue formation; in four cases this was associated with permanently displaced and deformed disks. All five joints were refractory to nonsurgical treatment. Surgically extirpated hyperplastic tissue and disk attachments contained nerve fibers and thickened adventitia of vessels, resulting in narrowed or obliterated lumina, extravasated erythrocytes, and fibrinlike deposits. The synovial membrane showed fibrinoid necrosis or was lost. The pain reaction in temporomandibular joints with hyperplastic soft-tissue formation may be released by compression or tension of nerves, breaking down products from blood or tissue ischemia. Contrast filling of both joint spaces, combined with tomography, was required for detection of the hyperplastic tissue formation.

Adult↗
PubMed1986

Internal derangement of the temporomandibular joint: radiographic and histologic changes associated with severe pain.

In 20 temporomandibular joints (TMJs) (15 patients) with internal derangement associated with severe pain, the presurgical radiographic findings were compared with the morphologic and histologic alterations. Disc extirpation was performed in 17 joints, and in three joints the disc was surgically repositioned. Deformation of the disc observed by double-contrast arthrotomography was verified histologically. Perforation of the posterior disc attachment was seen in two joints; both were associated with osteophyte formation and flattening of the articular eminence. The white disc-like structure in 11 cases was composed of an anterior, stiff, bulgy, biconvex structure combined with a posterior flattened portion that grossly was incorrectly determined to be part of the disc, but that was identified histologically as a posterior disc attachment that had undergone adaptive change characterized by connective tissue hyalinization. In the arthrotomogram the disc position could easily be determined. However, the disc-like clinical appearance of the posterior disc attachment in these cases made determination of disc position at surgery uncertain or impossible. The nonhyalinized posterior disc attachment was intensely red and showed advanced histologic alterations of the vessels, deposits of extravasated erythrocytes and fibrin, and altered composition of the connective tissue. Thus, signs of inflammation were present but without activation of the local immune system since no major inflammatory cell infiltrates were seen. Small accumulations of lymphocytes were seen in only two cases. The surgically extirpated posterior attachments were innervated by silver-positive nerve fibers ranging in diameter from 1 to 15 micron. The severe pain in the TMJs is likely to have originated from this innervated posterior disc attachment or capsule and to have been triggered by the vascular reaction.

Adult↗
PubMed1986

Distribution of substance P-like immunoreactive nerve fibers in temporomandibular joint soft tissues of monkey.

The distribution of substance P-immunoreactive and silver impregnated nerve fibers in the temporomandibular joint soft tissues of the Macaca fascicularis monkey was investigated in frozen sections. The pattern of substance P-immunoreactive structures in the soft tissues and periosteum of the temporomandibular joint was compared with the distribution of silver impregnated nerve fibers within these tissues. Presence of substance P-immunoreactive fibers was demonstrated in the temporomandibular joint capsule, disc attachments, fascia, adjacent periosteum and within the interfascicular connective tissue of the lateral pterygoid muscle. The overall distribution corresponded to that of silver impregnated nerve fibers. Substance P-immunoreactive nerve fibers were found in the adventitia of arteries in all vascularized temporomandibular joint soft tissues but could not be found in the adventitia of veins. No substance P-immunoreactive or silver impregnated nerve fibers were seen in the dense collagenous tissue forming the disc. Substance P is suggested to influence the major features of inflammation and to play a role in acute and chronic pain conditions.

Animals↗
PubMedDate not supplied

Testing shelled corn for aflatoxin, Part I: estimation of variance components.

The variability associated with testing lots of shelled corn for aflatoxin was investigated. Eighteen lots of shelled corn were tested for aflatoxin contamination. The total variance associated with testing shelled corn was estimated and partitioned into sampling, sample preparation, and analytical variances. All variances increased as aflatoxin concentration increased. With the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentration. Test results on a lot with 20 parts per billion aflatoxin using a 1.13 kg sample, a Romer mill, 50 g subsamples, and liquid chromatographic analysis showed that the total, sampling, sample preparation, and analytical variances were 274.9 (CV = 82.9%), 214.0 (CV = 73.1 %), 56.3 (CV = 37.5%), and 4.6 (CV = 10.7%), respectively. The percentage of the total variance for sampling, sample preparation, and analytical was 77.8, 20.5, and 1.7, respectively.

Aflatoxins↗