Search PubMed⌕ Search

Biomedical subjects

J Charlier

Publications and source records attributed to J Charlier.

At least 55 records · Page 3Linked to original sources
PubMed1987

Lysyl-tRNA synthetase from Escherichia coli K12. Chromatographic heterogeneity and the lysU-gene product.

In contrast with most aminoacyl-tRNA synthetases, the lysyl-tRNA synthetase of Escherichia coli is coded for by two genes, the normal lysS gene and the inducible lysU gene. During its purification from E. coli K12, lysyl-tRNA synthetase was monitored by its aminoacylation and adenosine(5')tetraphospho(5')adenosine (Ap4A) synthesis activities. Ap4A synthesis was measured by a new assay using DEAE-cellulose filters. The heterogeneity of lysyl-tRNA synthetase (LysRS) was revealed on hydroxyapatite; we focused on the first peak, LysRS1, because of its higher Ap4A/lysyl-tRNA activity ratio at that stage. Additional differences between LysRS1 and LysRS2 (major peak on hydroxyapatite) were collected. LysRS1 was eluted from phosphocellulose in the presence of the substrates, whereas LysRS2 was not. Phosphocellulose chromatography was used to show the increase of LysRS1 in cells submitted to heat shock. Also, the Mg2+ optimum in the Ap4A-synthesis reaction is much higher for LysRS1. LysRS1 showed a higher thermostability, which was specifically enhanced by Zn2+. These results in vivo and in vitro strongly suggest that LysRS1 is the heat-inducible lysU-gene product.

Adenine Nucleotides↗
PubMed1986

alpha-Difluoromethylornithine induces protective immunity in mice inoculated with Plasmodium berghei sporozoites.

Mice inoculated weekly with Plasmodium berghei sporozoites while under treatment with alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, developed protective immunity against subsequent challenge with this parasite. The percentage of mice protected was similar whether DFMO alone (55%) or DFMO + chloroquine (65%) was used. With chloroquine alone, only 12% of mice were protected. This protection was long-lasting (at least six months). The immunity protected against sporozoites but not against erythrocytic form inoculation. It is suggested that this protection is induced by antigens released from exoerythrocytic schizonts whose further development is inhibited by DFMO.

Animals↗
PubMed1985

[Methods of stimulation in visual electrophysiology].

After introducing physical and physiological stimulation parameters, the authors present different techniques and discuss their clinical usefulness for the investigation of the visual system: flashes: chiefly 'ganzfeld' stimulators (whole field or local stimulation). A solution using optic fibres incorporated in a sclero-corneal electrode built in our laboratory is presented; patterns: bars or chekerboards, especially on TV screens. Advantages and inconveniences of video images are discussed; other techniques: essentially endocular laser interference fringes, electrical stimulations, high level flashes for ERP and binocular studies, particularly dynamic random dot pattern EVP. In conclusion, the necessity for the careful control of stimulation characteristics and for a strategy suitable for clinical examination is discussed.

Brain↗
PubMed1983

Plasmodium berghei: inhibition of the sporogonous cycle by alpha-difluoromethylornithine.

alpha-Difluoromethylornithine (DFMO), an enzyme inhibitor of ornithine decarboxylase, inhibits the sporogonous cycle of the malaria parasite Plasmodium berghei in the mosquito vector Anopheles stephensi. DFMO was administered to the mosquitoes dissolved either in the sugar solution at their disposal in the cages or through blood meals taken from treated mice. The mice subsequently bitten by mosquitoes treated with DFMO by both routes of administration did not contract malaria.

Animals↗
PubMed1982

Transcription of Regions within the divergent argECBH operon of Escherichia coli: evidence for lack of an attenuation mechanism.

Using in vitro and in vivo assays, we could detect no early termination of DNA transcription in the proximal part of the argCBH arm of the argECBH divergent operon. The discrepancy noted previously between the respective amplitudes of variation of messenger and enzyme synthesis must therefore be attributed to other causes than a difference in efficiency between attenuation and repression.

Bacteriophage lambda↗
PubMed1982

Arginyl-tRNA synthetase from Escherichia coli K12: specificity with regard to ATP analogs and their magnesium complexes.

Fifteen analogs of ATP have been tested in the ATP/PPi pyrophosphate exchange and the aminoacylation of arginyl-tRNA synthetase from E. coli K12. Six compounds are substrates in both reactions, whereas seven of the triphosphates were inhibitors for both reactions. The Km, V and Ki values have been determined. The enzyme is less specific against base modifications of the ATP molecule than arginyl tRNA synthetase from baker's yeast in the aminoacylation and is inhibited by more base-modified compounds in the ATP/PPi exchange. The enzyme accepts 3'-deoxy-ATP as substrate and is inhibited by 2'-methoxy-ATP, whereas the reversed observation is made for the yeast arginyl-tRNA synthetase. The stoichiometry and association constants of complexes formed by six ATP analogs (four substrates and two inhibitors) and magnesium ions were investigated; five analogs form 1:1 complexes, one analog (3'-deoxy-ATP) binds two magnesium ions. The enzyme must accept different complexes formed with one or two magnesium ions as substrate, which must be different in structure from complexes proposed in literature.

Adenosine Triphosphate↗
PubMed1982

[Total right hemispherectomy: neurophysiological study after twenty-six years].

Twenty-six years after a total right hemispherectomy for tumor when thirteen years old, a right-handed patient presented with disturbances of equilibrium, urinary incontinence, and a marked reduction in motor impulses, in spite of a subnormal intelligence quotient (0.85). Computed tomography examinations suggested the presence of a normal pressure hydrocephalus. However intracranial pressure monitoring and isotopic and cerebrospinal fluid perfusion tests showed the absence of any cerebral obstruction, and free communication between the cerebral and spinal spaces, though intracranial volume capacity accommodation was greatly reduced. Clinical examination demonstrated good quality sensory appreciation by the left half of the body, the possibility of detecting an object in the visual hemifield supposedly blind, and perfect location of a sound source. Somesthetic evoked potentials were studied by stimulating the median nerve in the left and right wrist regions. Left hemisphere evoked potentials from a contralateral stimulus, were of normal latency, amplitude and morphology, the response to an ipsilateral stimulus also presenting an early potential component (N 26 starting at N 21). This exceptional finding in a hemispherectomized patient could be related to activity of the spinoreticulothalamic tracts in the lemniscal or extralemniscal systems. Auditory function tests demonstrated perfect stereoaudiometry and the quality of perception during dichotic listening tests. Auditory evoked potentials in the brain stem included only minor functional-type anomalies, with slightly increased latencies in the pons on the left, and the mesencephalon and pons on the right. The presence of a bilateral wave VI was related to activity of the median geniculate pathway. Visual function tests showed good quality left photomotor reflexes and positive object detection in the anopsic hemifield. Results of these tests were reproducible during the same examination and after an interval of several months. The relevant literature is reviewed.

Adolescent↗
PubMed1979

Arginyl-tRNA synthetase from Escherichia coli K12. Purification, properties, and sequence of substrate addition.

Arginyl-tRNA synthetase from Escherichia coli K12 has been purified more than 1000-fold with a recovery of 17%. The enzyme consists of a single polypeptide chain of about 60 000 molecular weight and has only one cysteine residue which is essential for enzymatic activity. Transfer ribonucleic acid completely protects the enzyme against inactivation by p-hydroxymercuriben zoate. The enzyme catalyzes the esterification of 5000 nmol of arginine to transfer ribonucleic acid in 1 min/mg of protein at 37 degrees C and pH 7.4. One mole of ATP is consumed for each mole of arginyl-tRNA formed. The sequence of substrate binding has been investigated by using initial velocity experiments and dead-end and product inhibition studies. The kinetic patterns are consistent with a random addition of substrates with all steps in rapid equilibrium except for the interconversion of the cental quaternary complexes. The dissociation constants of the different enzyme-substrate complexes and of the complexes with the dead-end inhibitors homoarginine and 8-azido-ATP have been calculated on this basis. Binding of ATP to the enzyme is influenced by tRNA and vice versa.

Amino Acids↗
PubMed1979

Adenosine triphosphate consumption by bacterial arginyl-transfer ribonucleic acid synthetases.

ATP consumption by arginyl-tRNA synthetases from Escherichia coli and Bacillus stearothermophilus has been investigated by the firefly luciferin--luciferase assay. Arginyl-tRNA synthetase from E. coli utilizes ATP only for aminocylation of tRNA with a 1:1 stoicheiometry. In contrast, we have shown an adenosine triphosphatase activity of arginyl-tRNA synthetase from B. stearothermophilus in the absence of tRNAArg. Dowex chromatography revealed the formation of ADP by the thermophile enzyme; under aminoacylation conditions, AMP was also formed in amounts stoicheiometric with arginyl-tRNA formation.

Adenosine Triphosphate↗
PubMed1976

Arginyl-tRNA synthetase from Escherichia coli. Influence of arginine biosynthetic precursors on the charging of arginine-acceptor tRNA with [14C]arginine.

The behaviour of arginyl-tRNA synthetase (EC 6.1.1.19) in the presence of the arginine biosynthetic precursors, argininosuccinate, ornithine and citrulline, was studied in several Escherichia coli K12 strains and in E. coli W. The results of kinetic measurements with partially purified extracts indicate that the arginyl-tRNA synthetase of E. coli is not inhibited by the arginine precursors. The apparent affinity constant Km for arginine of the K12 enzyme is about 3.4 muM in the absence and in the presence of these precursors, whereas the W enzyme an apparently slightly lowered Km and a decreased [14C]arginyl-tRNA equilibrium level in the presence of argininosuccinate. This however was shown to be due to isotopic dilution of [14C]arginine by non-radioactive amino acid formed from argininosuccinate by argininosuccinate lyase (EC 4.3.2.1) contaminating the synthetase preparation. This finding emphasizes the necessity of using pure arginyl-tRNA synthetase in order to study the possible regulatory involvement of this enzyme in the control of the arginine regulon in vitro.

Amino Acyl-tRNA Synthetases↗