PubMed Health⌕ Search

Biomedical subjects

A Becker

Publications and source records attributed to A Becker.

At least 73 records · Page 4Linked to original sources
PubMed1996

Promoter analysis of the Xanthomonas campestris pv. campestris gum operon directing biosynthesis of the xanthan polysaccharide.

The Xanthomonas campestris gum gene cluster is composed of 12 genes designated gumB, -C, -D, -E, -F, -G, -H, -I, -J, -K, -L, and -M. The transcriptional organization of this gene cluster was analyzed by the construction of gum-lacZ transcriptional fusions in association with plasmid integration mutagenesis. This analysis, coupled with primer extension assays, indicated that the gum region was mainly expressed as an operon from a promoter located upstream of the first gene, gumB.

Base Sequence↗
PubMed1996

Changes in peak flow, symptom score, and the use of medications during acute exacerbations of asthma.

Changes in symptom score and peak expiratory flow (PEF) and the use of medications during the first acute exacerbation of asthma were studied in 41 patients and matched controls who took part in a panel study. An acute exacerbation was defined as the presence of at least one of the following: any unscheduled physician visit, visit to an emergency room, or hospitalization for treatment of asthma; a decrease in PEF by 30% from the patient's best reading; an increase in asthma symptoms during the day and night for over 48 h and not responding to usual medications; and the commencement or doubling of the dose of oral or inhaled steroids for any of the foregoing reasons. Data from -9 to -7 d before the onset of an acute exacerbation were taken as the baseline data, with which the values of the subsequent 14 d were compared. Significant increases in symptoms occurred before a significant reduction in PEF. None of the patients had a decrease of more than 30% in PEF before the onset of symptoms. Daily variation in PEF was not significantly increased from the baseline. Our results suggest that PEF monitoring is not as sensitive as a symptom diary for revealing acute exacerbations of asthma, and that a 30% decrease in PEF is too stringent a criterion for defining an acute exacerbation.

Acute Disease↗
PubMed1996

Serum sex hormone-binding globulin and osteocalcin in systemic nonthyroidal illness associated with low thyroid hormone concentrations.

To test the hypothesis that patients with systemic nonthyroidal illness (NTI) and impaired thyroid hormone metabolism most commonly present with the low T3 or low T4 syndrome are in an euthyroid status at the tissue level, we determined serum sex hormone-binding globulin (SHBG) and osteocalcin (OC) as parameters for thyroid hormone availability to liver and bone. Serum SHBG and OC concentrations were measured in 61 severely ill patients with decreased serum levels of either T3 alone (n = 47) or both T3 and free T4 (n = 14). None of the patients had primary thyroid disorder indicated by regular thyroid sonomorphology and normal basal TSH concentrations. Data were compared with values obtained from age- and sex-matched controls without impairment of thyroid hormone physiology. The respective results from the study groups and from control subjects were as follows: low T3 SHBG, 49 +/- 30 nmol/L; low T4 SHBG, 35 +/- 14 nmol/L; control SHBG, 45 +/- 28 nmol/L; low T3 OC, 0.87 +/- 0.75 nmol/L; low T4 OC, 0.75 +/- 0.71 nmol/L; control OC, 0.98 +/- 0.87 nmol/L. SHBG and OC do not differ significantly between NTI patients with low T3 or low T4 syndrome and controls, and no significant relationship was found between thyroid hormone parameters and SHBG or OC, respectively. We conclude that the term euthyroid sick syndrome applied for the condition of systemic NTI associated with reduced circulating thyroid hormone concentrations appears to be appropriate at the level of hepatocytes and osteoblasts. Data are in partial contradiction to the results of previous studies using alternative serum parameters for assessment of peripheral thyroid hormone action (e.g. angiotensin-converting enzyme). Due to the tissue specificity of the biochemical serum markers, conflicting results may be explained by organ-specific differences in local thyroid hormone exposure. In case of doubt, SHBG and OC determinations may help specify peripheral thyrometabolic status in NTI.

Adult↗
PubMed1996

Neonatal characteristics as risk factors for preschool asthma.

Childhood asthma usually begins early in life. Neonatal characteristics are reportedly predictive of symptom onset. This investigation utilized data from a provincial health organization to evaluate the effect of several birth characteristics on asthma incidence and hospitalization for asthma during age 0-4. Using logistic regression, the odds ratios (OR) for the following variables indicate a significant (p < 0.05) association with physician-diagnosed preschool asthma: male gender (OR = 1.72), birthweight < 1500 g (OR = 2.11), prematurity (OR = 1.34), respiratory distress syndrome (RDS) in the presence (OR = 2.95) or absence (OR = 1.61) of bronchopulmonary dysplasia (BPD), and transient tachypnea of the newborn (TTN; OR = 1.36). Male gender (OR = 1.91), birthweight < 1500 g (OR = 2.56), RDS with and without BPD (OR = 3.35 and 2.50, respectively), TTN (OR = 2.08), and severe birth asphyxia (OR = 1.94) showed an important association with hospitalization due to asthma. Neonatal characteristics are important determinants for the risk of preschool asthma, even after mutual adjustment.

Asthma↗
PubMed1996

Critical role of the sinuses of Valsalva in the durability of valved conduits.

BACKGROUND AND AIMS OF THE STUDY: Most work in search of an ideal extracardiac valved conduit has assumed that the type of tissue used for construction is the determining factor for its behavior and durability. The excellent results of our study with a valved conduit incorporating sinuses of Valsalva and made of autologous pericardium showed that the design plays a crucial role in addition to the type of material. MATERIALS AND METHODS: We report the experimental results of three different pericardial sinus bearing valved conduits made of 0.5% glutaraldehyde treated autologous pericardium (Group 1), dye mediated photooxidized bovine pericardium (Group 2), and glutaraldehyde treated bovine pericardium (Group 3) implanted in the right ventricular outflow tract of sheep. Groups 1, 2 and 3 had 11, 11 and four animals available for assessment out of 12, 18 and six implantations respectively. The valved conduits were explanted at varying intervals between one and 11 months. The conduit function was assessed with hemodynamic, echocardiographic and Doppler studies both at the time of implantation and sacrifice. The explanted conduit was studied macroscopically and subjected to histopathologic examination. RESULTS: The hemodynamic and echocardiographic studies at implantation showed very satisfactory results in all three groups. At the time of sacrifice, Group 1 showed consistently good results. In a significant number of animals in Groups 2 and 3, one, two or even three cusps had become adherent to the conduit wall, resulting in severe regurgitation. The sinuses were well preserved in Group 1, while they were less prominent in Group 2 and least in Group 3. Histopathologically, the three groups basically showed the same feature, a process of fibrocellular proliferation resulting in thickening. In this study the adhesion of the cusps to the sinus wall was related to the degree of prominence of the sinuses of Valsalva, which in turn depended on the ability to shape the pericardium at the time of construction of the valved conduit. CONCLUSIONS: This study stresses the importance of the sinuses in the behavior of the semilunar valve leaflets.

Animals↗
PubMed1996

Analysis of the complementary determining region III of the immunoglobulin heavy chain locus in acute lymphoblastic leukemia in Chilean children.

We have analyzed the sequence of 40 VDJ rearrangements of the immunoglobulin heavy chain gene locus on 32 unselected children from Chile with precursor B cell ALL at diagnosis. Rearrangements were derived by PCR with VH gene family-specific primers and sequenced directly. The number of VDJ rearrangements, and the pattern of VH, DH and JH gene usage was identical to the one reported by groups from developed countries. CDR3 regions represented an unbiased repertoire; VH to JH joinings were in frame in 36% of cases. Absent N nucleotides in the DJ border, suggestive of fetal origin of ALL, were seen in 9/40 rearrangements but they did not correlate with younger age. More than one rearrangement was sequenced in six patients, representing independent events with no signs of clonal evolution. One patient was analyzed at first bone marrow relapse showing persistence of one rearrangement and evolution of a second one which conserved the DJ border. The subset of B cell precursors which suffer malignant transformation to ALL appear to be common in different parts of the world.

Adolescent↗
PubMed1995

Extension of the Rhizobium meliloti succinoglycan biosynthesis gene cluster: identification of the exsA gene encoding an ABC transporter protein, and the exsB gene which probably codes for a regulator of succinoglycan biosynthesis.

Two new genes, designated exsA and exsB, were identified adjacent to the 24 kb exo gene cluster of Rhizobium meliloti, which is involved in succinoglycan (EPS I) biosynthesis. The derived amino acid sequence of ExsA displayed significant homologies to ATP binding cassette (ABC) transporter proteins. R. meliloti strains mutated in exsA were characterized by a decreased ratio of HMW to LMW EPS I, indicating a function for ExsA in EPS I biosynthesis. The R. meliloti NdvA protein, which is involved in the transport of cyclic beta-(1,2)-glucans, was identified as the closest homologue of ExsA. R. meliloti exsB mutants produced a three-fold increased amount of EPS I in comparison to the wild-type strain. In contrast, high copy number of exsB resulted in a decrease in the EPS I level to 20% of wild type, indicating that the exsB gene product can negatively influence EPS I biosynthesis. It was demonstrated that this influence is not due to transcriptional regulation of the exo genes by the exsB gene product. By plasmid integration it was shown that exsA and exsB represent monocistronic transcription units.

ATP-Binding Cassette Transporters↗
PubMed1995

Interaction of terminase, the DNA packaging enzyme of phage lambda, with its cos DNA substrate.

Terminase, the DNA packaging enzyme of phage lambda is an ATP-stimulated, site-specific endonuclease comprising the products of lambda genes Nu1 and A. The interaction of terminase with its specific DNA substrate cos was studied by footprinting. cos (the DNA segment R4-cosN-R3R2R1), situated at the chromosomal junctions in a concatemer, consists of a nicking domain (cosN) where terminase nicks DNA to regenerate the 12-base cohesive ends of the mature lambda chromosome and a binding domain (cosB) that includes four 16-base-pair repeat sequences, R1, R2 and R3 to the right of cosN and R4 (now called cosQ and not, in strict definition, part of cosB) to the left of cosN. We show that terminase molecules bind asymmetrically to the two ends of the chromosome. Binding to the right of cosN is stimulated by ATP, whereas binding to the left of cosN is strictly dependent upon ATP. When cosN is deleted and ATP is withheld, terminase molecules bind exclusively to the R3, R2 and R1 sites via their gpNu1 subunits. An invariant R-site GG doublet is protected from methylation in both R3 and R2, showing the location of major-groove close contacts upon binding. Terminase's interactions with DNAs that include all of cos are more extensive and are influenced by ATP; not only are the R sites protected, but so is the DNA between them, as well as cosN, the cosN-R3 region, R4 and sequences to the left of R4. The pattern suggests an highly organized protein-DNA continuum involving several terminase molecules and several hundred base-pairs of DNA, suitably named the termisome. Evidence is given that this assembly is dependent on the interaction of ATP with the gpA subunit of terminase.

Adenosine Triphosphate↗
PubMed1995

New gentamicin-resistance and lacZ promoter-probe cassettes suitable for insertion mutagenesis and generation of transcriptional fusions.

A set of antibiotic-resistance and promoter-probe cassettes suitable for insertion mutagenesis and generation of transcriptional fusions was constructed. The cassettes contain the aacC1 gene of transposon Tn1696 conferring resistance to gentamicin in a large variety of Gram- and Gram+ bacteria. In addition to the antibiotic-resistance gene, a promoterless Escherichia coli lacZ gene was included in the cassettes, allowing the determination of the transcriptional activity at the insertion site. The cassettes can be excised from a plasmid mediating ampicillin resistance by many commonly used restriction enzymes. The new constructs have been successfully used for mutagenesis and studies of gene transcription in Rhizobium meliloti.

Acetyltransferases↗
PubMed1995

N omega-nitro-L-arginine methyl ester interferes with pentylenetetrazol-induced kindling and has no effect on changes in glutamate binding.

The effects of N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, on seizure development and processes of glutamate neurotransmission were studied in the pentylenetetrazol (PTZ)-kindled rats. For this purpose, a dose of 10 mg/kg L-NAME was injected prior to the 13 kindling stimulations. Eight days after the final injection, glutamate binding to brain membranes was measured. It was shown that L-NAME suppressed the kindling development significantly. Furthermore, L-NAME-pretreated rats showed lower seizure scores in reaction to a challenge dose of PTZ. However, glutamate binding was not changed by the pretreatment. The data suggest an involvement of NO in the mechanisms related with kindling.

Animals↗
PubMed1995

Expression of active recombinant pallidipin, a novel platelet aggregation inhibitor, in the periplasm of Escherichia coli.

The platelet aggregation inhibitor pallidipin is a protein present in the saliva of the blood-sucking triatomine bug Triatoma pallidipennis. Expression of recombinant pallidipin in the periplasm of Escherichia coli was achieved by placing its coding sequence downstream of the alkaline phosphatase (APase) or trc promoter in frame with bacterial leader peptide DNA sequences derived from APase or from the periplasmic form of cyclophilin (Cph). In each case the DNA sequence of mature pallidipin was merged to the leader peptide coding part, either directly, or while introducing additional amino acids, in order to assess their influence on the activity of the leader peptidase and on the biological activity of the recombinant protein. All tested constructs gave rise to abundant periplasmic expression of pallidipin, which was then purified by a combination of cation- and anion-exchange chromatography followed by size-exclusion gel chromatography. Recombinant pallidipin had the expected molecular mass (approximately 19 kDa) and was correctly processed, as demonstrated by SDS/PAGE and N-terminal amino acid sequencing. The highest expression levels were obtained with the three APase-derived expression plasmids. Platelet aggregation tests revealed that E. coli-derived pallidipin was fully active, with an IC50 of 33-89 nM, comparable with that of the native protein, except when an additional N-terminal lysyl-isoleucyl dipeptide was present, which resulted in an IC50 more than ten times higher.

Amino Acid Sequence↗
PubMed1995

Mouse androgen-dependent epididymal glycoprotein CRISP-1 (DE/AEG): isolation, biochemical characterization, and expression in recombinant form.

In the rat, the secretory glycoprotein DE/AEG is one of the main constituents of the epididymal fluid. We have recently reported the cloning of the cDNA for the related cysteine-rich secretory protein-1 (CRISP-1) from murine epididymis (Haendler et al., 1993; Endocrinology 133:192-198). The protein has now been isolated from the same organ and its N-terminal amino acid sequence has been determined. CRISP-1 exhibited an isoelectric point of approximately 6.8. High levels of CRISP-1 antigen were detected in the corpus and cauda of the epididymis, vas deferens, seminal vesicle, prostate, and in the salivary gland by immunohistochemistry. A quantitative analysis of the cauda epididymal fluid by sandwich ELISA revealed that CRISP-1 represented approximately 15% of the total protein. For heterologous expression, the CRISP-1 coding sequence was introduced into the pMPSV/CMV vector before transfection of baby hamster kidney (BHK) cells and selection with puromycin and neomycin. Expression in insect cells was achieved by co-transfection of Sf9 cells with a transfer vector and baculovirus DNA. Recombinant CRISP-1 was isolated in quantities sufficient for structural analysis. Ethyl maleimide treatment showed that all 16 cysteines were engaged in disulfide bonds. Proteolytic digestion demonstrated that the six cysteines localized in the N-terminal moiety formed three bonds with each other, suggesting the existence of two discrete domains in the protein.

Amino Acid Sequence↗
PubMed1995

PTZ-kindling after colchicine lesion in the dentate gyrus of the rat hippocampus.

Pentylenetetrazol (PTZ)-kindling represents a model of a primarily generalized epilepsy. We investigated the role of the dentate gyrus of the hippocampus in this model of epilepsy by destruction of this structure by colchicine, injected in the dorsal and ventral hippocampus of rats. After a period of 7 days PTZ-kindling was started. The kindling development was slightly accelerated in colchicine treated animals compared to control rats. After kindling completion the learning performance of the rats was tested in a shuttle-box experiment. The learning deficit found in fully kindled rats was not influenced by colchicine pretreatment. However, colchicine itself impaired the learning performance of rats in the shuttle-box.

Animals↗
PubMed1995

Antiepileptic drugs--their effects on kindled seizures and kindling-induced learning impairments.

Many epileptic patients suffer from cognitive impairments. These impairments may be a consequence of the epileptogenic process and/or antiepileptic medication. Kindling is considered a useful experimental model to investigate drug effects on both the convulsive component of epilepsy and related alterations at the behavioral level. In our experiments, kindling was induced by repeated injections of pentylenetetrazol (PTZ). To test the effect of antiepileptic drugs on kindled seizures and kindling-induced learning deficits we injected ethosuximide, dipropylacetate, and phenobarbital prior to each kindling stimulation or after kindling completion, and tested these animals in a shuttle-box paradigm. Dipropylacetate and phenobarbital suppressed the development of motor seizures and counteracted the learning deficit. Although ethosuximide had a clear effect on kindled seizures, the learning deficit occurred in kindled rats. This suggests that AEDs effects on kindled seizures are not correlated with the elimination of deficits in the field of cognition.

Animals↗
PubMed1995

Flunarizine--its effect on pentylenetetrazol-kindled seizures and on related cognitive disturbances.

Epileptics are often faced with impaired intellectual processes. The basis of these impairments is still poorly understood. Kindling is an accepted model for the study of the convulsive component of epilepsy. Furthermore, it was demonstrated that pentylenetetrazol-kindled rats show diminished shuttle-box learning. Therefore, we used this model to study the influence of flunarizine, a calcium antagonist, on kindled seizures as well as related learning impairments. It was found, that acutely administered flunarizine significantly suppressed the expression of kindled seizures, but there was no effect on the developmental character of kindling. Moreover, the substance had an anticonvulsant action when administered after completion of kindling. The learning ability of kindled rats was significantly augmented when flunarizine was injected prior to each convulsive stimulation or when administered after completion of kindling. The results were explained in terms of interactions of a depressive effect on abnormal neuronal excitation, a protection against calcium-induced neurotoxicity and, finally, the vascular effect of flunarizine.

Animals↗