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Biomedical subjects

A Becker

Publications and source records attributed to A Becker.

At least 307 records · Page 17Linked to original sources
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↗
PubMed1995

Gq alpha protein function in vivo: genetic dissection of its role in photoreceptor cell physiology.

Heterotrimeric G proteins mediate a variety of signaling processes by coupling seven-transmembrane receptors to intracellular effector molecules. The Drosophila phototransduction cascade is a G protein-coupled signaling cascade that utilizes a phospholipase C (PLC beta) effector. PLC beta has been shown to be activated by Gq alpha in reconstituted systems. To determine whether a Gq-like protein couples rhodopsin to PLC, and to study its function, we isolated a mutant defective in a photoreceptor-specific Gq protein, DGq. We now demonstrate that Gq is essential for the activation of the phototransduction cascade in vivo. We also generated transgenic flies expressing DGq under an inducible promoter and show that it is possible to manipulate the sensitivity of a photoreceptor cell by controlled expression of DGq. Characterization of quantum bumps in mutants expressing less that 1% of the levels of DGq revealed that the rhodopsin-G protein interaction does not determine the gain of the single photon responses. Together, these results provide significant insight into the role of Gq in regulating the output of a photoreceptor cell.

Amino Acid Sequence↗
PubMed1995

Nootropic drugs have different effects on kindling-induced learning deficits in rats.

Kindling represents an accepted model of human epileptogenesis. Furthermore, it has been demonstrated that kindled rats show a diminished learning performance in an active avoidance task. In our study we administered different nootropic drugs to kindled rats to test their effects on learning a two-way active avoidance task in the shuttle-box. Kindling was induced by repeated intraperitoneal injections of 45 mg kg-1 pentylenetetrazol (PTZ) once every 48 h. The substances vinpocetine (0.1 and 1.0 mg kg-1), methylglucamin orotate (225 and 450 mg kg-1), piracetam (100 mg kg-1), and meclofenoxate (100 mg kg-1) were administered during kindling development and after kindling completion prior to each session in the learning experiment. The nootropic drugs had little if any effect on severity of seizures. Concerning their effect on learning the substances each acted in a specific manner. Methylglucamin orotate enhanced the learning deficit induced by kindling. Meclofenoxate injected prior to the kindling stimulation was ineffective, whereas administration prior to the learning test improved the learning performance effectively. A complementary action was shown in experiments with vinpocetine. Only piracetam prevented the occurrence of kindling-induced learning deficits regardless the administration schedule.

Animals↗
PubMed1995

In defense of the guidance theory of palatal canine displacement.

From the foregoing debate it will be quite clear that Peck et al. have provided ample evidence that may be used to fuel the arguments of both sides: 1. Their material does not contradict the possibility that environmental factors may give rise to palatal displacement of canines generated by genetic anomaly of the adjacent teeth. 2. The buccally displaced canine finds itself similarly environmentally compromised by the different factor of crowding which leads to its characteristic buccally ectopic guidance pattern. 3. (a) Canines that are transposed with the premolar, (b) others that have erupted ectopically, high in the buccal sulcus and in the absence of crowding, and (c) certain palatal canines whose root apex is located markedly distant from their designated site, may all be labeled as genetically controlled with a fair degree of confidence. 4. In between these clearly defined entities there exists a "gray area" in which it is probable that the etiology of the individual displaced teeth may be linked to a combination of circumstances that obey premise number 1 and premise number 2, to varying degrees. The guidance theory cannot provide the complete answer to the etiology of the palatally displaced canine. Were this so, we would find PDC every time there was an anomalous or missing lateral incisor. Equally, it may not yet be discounted out of hand and certainly not on the basis of the evidence provided in the article in question.

Cuspid↗
PubMed1995

[Effect of a supplemental Aspergillus niger phytase on the utilization of plant phosphorus by rainbow trout (Oncorhynchus mykiss)].

Effects of a supplemental Aspergillus niger-phytase on digestibility and utilization of dietary phosphorus (P) were studied in three experiments with rainbow trout. P concentration in the diets was 4.8 and 5.8 g/kg DM, respectively. The P contained in the diet originated solely from plants, mainly soy-products. Digestibility of P was studied using the stripping method and hydrochloride insoluble ash as marker. Utilization was studied in growth trials by use of the comparative body analysis. At a water temperature of 15 degrees C, both digestibility and utilization of P were increased from 25 to 57% and from 17 to 49%, respectively when 1000 U/kg phytase were supplemented. Feed consumption and gain of trout were significantly increased. At a water temperature of 10 degrees C, utilization of P was also increased from 6 to 25%. However, feed consumption and gain of trout were very low at this water temperature and not influenced by the supplemental phytase.

6-Phytase↗
PubMed1995

House dust mite allergen levels in two cities in Canada: effects of season, humidity, city and home characteristics.

The homes of 120 patients with asthma, 57 in Vancouver and 63 in Winnipeg, were studied. The characteristics of the homes were assessed by a questionnaire. Dust samples were collected and the indoor relative humidity was measured four times during the year covering all four seasons in both cities. Mite allergen levels were determined using monoclonal antibodies against Der p I and Der f I by the ELISA method. The mean levels of both mite allergens in mattress and floor samples in the homes in Vancouver and in Winnipeg were relatively low for all seasons. Mite allergen levels were found to be associated with city, season and individual home differences. They were significantly higher in Vancouver than in Winnipeg. Der p I and Der f I in mattress samples in both cities and Der f I in floor samples in Vancouver, varied by season. The indoor relative humidity level in the homes in Vancouver were also significantly higher than those in Winnipeg. There was, however, no significant association between the levels of indoor relative humidity and the levels of mite allergens after adjusting for variations in city, season and individual home. Although individual home differences were highly associated with mite allergen levels, only a few home characteristics were found to be related to mite allergen levels such as the type and the age of the home, the type of heating, the use of feather pillows and the number of occupants in the homes. Whether low levels of mite allergens are partially responsible for the relatively low prevalence of childhood asthma in Canada remains to be investigated.

Allergens↗
PubMed1995

Low-molecular-weight succinoglycan is predominantly produced by Rhizobium meliloti strains carrying a mutated ExoP protein characterized by a periplasmic N-terminal domain and a missing C-terminal domain.

The membrane topology of the Rhizobium meliloti 2011 ExoP protein involved in polymerization and export of succinoglycan was analysed by translational fusions of lacZ and phoA reporter genes to the exoP gene. Based on this analysis, the ExoP protein could be divided into an N-terminal domain mainly located in the periplasmic space and a C-terminal domain located in the cytoplasm. Whereas the C-terminal domain of ExoP is characterized by a potential nucleotide-binding motif, the N-terminal ExoP domain contains the sequence motif 'PX2PX4SPKX11GXMXG', which is also present in proteins involved in the determination of O-antigen chain length. R. meliloti strains carrying mutated exoP* genes, exclusively encoding the N-terminal ExoP domain, produced a reduced amount of succinoglycan. This reduction could be suppressed by a mutation in the regulatory gene exoR. The ratio of low-molecular-weight to high-molecular-weight succinoglycan was significantly increased in the exoP* mutant strain. In the exoP*/exoR mutant strain only low-molecular-weight succinoglycan could be detected. Based on sequence homologies and similar hydropathic profiles, the N-terminal domain of ExoP was proposed to be a member of a protein family thought to be involved in polysaccharide chain-length determination.

Amino Acid Sequence↗
PubMed1995

Comparison of fresh and glutaraldehyde-treated autologous stented pericardium as pulmonary valve replacement.

The use of fresh autologous pericardium in valve surgery has shown poor results in the past mainly due to thickening and retraction. Recently, it has been suggested that a short treatment with glutaraldehyde might radically change its behavior. In an attempt to determine whether this disparity in results is due to the glutaraldehyde treatment or to a better present-day surgical technique, fresh and glutaraldehyde-treated autologous pericardium was mounted in a frame and implanted in the pulmonary position of adult sheep. Six survivors obtained in each group were sacrificed between 2 and 8 months in the "fresh" group and between 2 and 6 months in the "glutaraldehyde-treated" group. Macroscopically, the fresh pericardium became thickened and retracted in all specimens, eventually resulting in severe regurgitation, while the glutaraldehyde-treated, although slightly thickened, retained its pliability without significant retraction. Microscopically, viability of the central core of the collagen was more often preserved in the fresh pericardium. Endothelialization was irregular. In conclusion, short glutaraldehyde treatment seems to improve the results of autologous pericardium mounted on a valve stent. Its effect on calcification remains to be ascertained.

Animals↗
PubMed1995

[Efficacy of the granisetron/solumedrol combination in the control of drug-induced acute nausea and vomiting. Results of a prospective survey].

5 HT3 antagonist are effective drugs to control chemotherapy induced nausea and vomiting, but their optimum utilisation remain to be codify. In order to estimate efficacity of granisetron and solumedrol and to improve predictive factors of failure of antiserotoninergic agents, a prospective study have been realised 41 patients. During the first course of chemotherapy, 83% of patients presented less than two nausea and vomiting per day. Those results were the same from the first to the last course of chemotherapy. This study allowed to estimate anxiety of patients and maintain the hypothesis that more a antiemetic regimen is efficient less the predictive factors have a prognosis value.

Antiemetics↗