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Biomedical subjects

J Lapointe

Publications and source records attributed to J Lapointe.

At least 19 recordsLinked to original sources
PubMed1992

Preoperative coronary artery disease risk stratification based on dipyridamole imaging and a simple three-step, three-segment model for patients undergoing noncardiac vascular surgery or major general surgery.

A 3-step, 3-segment scintigraphic model was developed to improve the accuracy of dipyridamole-thallium imaging for preoperative cardiac risk assessment and to simplify the prognostic interpretation of the images. The model was developed in a pilot study of 60 patients and validated in a group of 355 patients referred for vascular and major general surgery. Study end points included myocardial infarction and cardiac death. Step 1: The postoperative cardiac event rate was 1.3% in 225 patients with normal anterior, inferio- and posterolateral segment perfusion and without transient left ventricular dipyridamole-induced cavitary dilation. Step 2: The physiologic rationale for step 2 consists of identifying patients who are most likely to have left main, 3-vessel or high-risk 2-vessel coronary artery disease or a significant amount of jeopardized myocardium in the territory of a critical coronary stenosis. Of 29 patients with either reversible defects of all 3 segments, transient cavitary dilation, or at least 1 severe grade 3/3 reversible defect, 52% (15 of 29) sustained a postoperative cardiac event. Step 3: The remaining 101 patients were stratified according to age greater than 70 years (p = 0.01), presence of diabetes (p = 0.0004) and the number of segments displaying reversible defects (1 or 2) with cardiac event rates ranging from 5 to 36%. The 3-step, 3-segment model is a useful alternative to the conventional interpretation of dipyridamole myocardial perfusion images for the purpose of quick and efficient preoperative risk stratification based on the rationale of correlating surgical risk with the amount of potentially ischemic myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Adenylosuccinate lyase of Bacillus subtilis regulates the activity of the glutamyl-tRNA synthetase.

In Bacillus subtilis, the glutamyl-tRNA synthetase [L-glutamate:tRNA(Glu) ligase (AMP-forming), EC 6.1.1.17] is copurified with a polypeptide of M(r) 46,000 that influences its affinity for its substrates and increases its thermostability. The gene encoding this regulatory factor was cloned with the aid of a 41-mer oligonucleotide probe corresponding to the amino acid sequence of an NH2-terminal segment of this factor. The nucleotide sequence of this gene and the physical map of the 1475-base-pair fragment on which it was cloned are identical to those of purB, which encodes the adenylosuccinate lyase (adenylosuccinate AMP-lyase, EC 4.3.2.2), an enzyme involved in the de novo synthesis of purines. This gene complements the purB mutation of Escherichia coli JK268, and its presence on a multicopy plasmid behind the trc promoter in the purB- strain gives an adenylosuccinate lyase level comparable to that in wild-type B. subtilis. A complex between the adenylosuccinate lyase and the glutamyl-tRNA synthetase was detected by centrifugation on a density gradient. The interaction between these enzymes may play a role in the coordination of purine metabolism and protein biosynthesis.

Adenylosuccinate Lyase↗
PubMed1992

Prognostic implications of a negative dipyridamole-thallium scan: results in 360 patients.

PATIENTS AND METHODS: A total of 360 patients with either normal perfusion (314) or fixed defects (46) on dipyridamole-thallium scans were followed over an average period of 16 months. Of the 360 patients, 194 subsequently underwent major noncardiac surgery. RESULTS: There were a total of eight cardiac events including two postoperative complications (one fatal and one nonfatal myocardial infarction) and six cardiac events during long-term follow-up (one sudden death and five nonfatal infarctions). During the follow-up period, three patients underwent coronary artery bypass surgery. The low cardiac event rate could not be explained by a low pretest likelihood of coronary artery disease: 77% of the 360 patients had either typical angina pectoris, a previous myocardial infarction, or peripheral vascular disease, which is associated with a high prevalence of coronary artery disease. CONCLUSIONS: In patients with a high pretest likelihood of coronary artery disease, the absence of thallium redistribution on a dipyridamole-thallium scan denotes a very low (1%) cardiac risk for major noncardiac surgery as well as low long-term cardiac mortality (0.3%) and morbidity (1.4%) rates. The coronary death rate is comparable to that of patients with minimal (less than 50%) coronary stenoses.

Clinical Protocols↗
PubMed1992

Higher specific activity of the Escherichia coli glutamyl-tRNA synthetase purified to homogeneity by a six-hour procedure.

The glutamyl-tRNA synthetase (EC 6.1.1.17) of Escherichia coli was purified to homogeneity from the overproducing strain DH5 alpha(pLQ7612) by a two-step procedure that takes only about 6 h and yields 10 mg of enzyme per gram of wet cells. The process consists of a two-phase polyethylene glycol-dextran partition, the top phase of which is diluted and directly applied to an anion-exchange FPLC MonoQ column. The purified enzyme has a specific activity about twice that of the same enzyme purified to homogeneity by the lengthy conventional procedure from either a normal strain or this overproducing strain. This difference is discussed in relation to the generation of microheterogeneity in proteins during their purification.

Bacterial Proteins↗
PubMed1991

Large scale sequencing projects using rapidly prepared double-stranded plasmid DNA.

We have developed a simple rapid plasmid DNA mini-preparation method which yields DNA of sufficient quality to be used in large scale sequencing projects. The method, which is a modification of the alkaline method of Birnboim and Doly (1979), requires less than two hours. We have eliminated the use of organic extractions, RNase digestion and alkaline denaturation of the DNA for annealing of the primer. The proportion of supercoiled plasmid DNA obtained is close to 100%. Greater than 80% of the clones yield at least 500 bp of sequence information per primer. The sequencing reactions from these double-stranded templates can be done on both strands using the universal and reverse sequence primers with the usual two reactions per primer, one to read close to the primer and one to read far from it. Thus, each clone yields at least 1 kb of sequence information. The preparation of the templates and the sequencing reactions can be done in less than three hours so that the sequencing gel can be run the same day.

Base Sequence↗
PubMed1990

Transient left ventricular cavitary dilation during dipyridamole-thallium imaging as an indicator of severe coronary artery disease.

Transient left ventricular (LV) cavitary dilation during dipyridamole-thallium imaging was reported in 45 of 510 (9%) consecutive patients referred for dipyridamole-thallium imaging. Clinical and hemodynamic effects observed during dipyridamole infusion were not predictive of transient cavitary dilation on the thallium images. Coronary angiography was performed in 32 of the 45 patients: 75% had either left main, 3-vessel or "high-risk" 2-vessel coronary artery disease. Although 25 of 45 patients (56%) with transient cavitary dilation were either asymptomatic or had only grade 1/4 effort angina, 16 of 25 patients (64%) not referred for coronary revascularization sustained a cardiac event during a mean follow-up of 12 months. Most events were cardiac deaths (75%) and 87% of events occurred within 4 months of the test. Noncardiac surgery was performed in 187 of the 510 patients. The postoperative cardiac event rate was 2% in the 101 patients with normal scans or fixed defects, 19% in 75 patients with reversible perfusion defects and 58% in 12 patients with reversible cavitary dilation (p less than 0.0001). Thus, transient LV dilation during dipyridamole-thallium imaging is a marker of severe underlying coronary artery disease, denotes a poor prognosis and predicts a high risk of postoperative cardiac complications in patients who undergo noncardiac surgery.

Coronary Angiography↗
PubMed1990

Glutamyl-tRNA synthetases of Bacillus subtilis 168T and of Bacillus stearothermophilus. Cloning and sequencing of the gltX genes and comparison with other aminoacyl-tRNA synthetases.

The glutamyl-tRNA synthetase (GluRS) of Bacillus subtilis 168T aminoacylates with glutamate its homologous tRNA(Glu) and tRNA(Gln) in vivo and Escherichia coli tRNA(1Gln) in vitro (Lapointe, J., Duplain, L., and Proulx, M. (1986) J. Bacteriol. 165, 88-93). The gltX gene encoding this enzyme was cloned and sequenced. It encodes a protein of 483 amino acids with a Mr of 55,671. Alignment of the amino acid sequences of four bacterial GluRSs (from B. subtilis, Bacillus stearothermophilus, E. coli, and Rhizobium meliloti) gives 20% identity and reveals the presence of several short highly conserved motifs in the first two thirds of these proteins. Conserved motifs are found at corresponding positions in several other aminoacyl-tRNA synthetases. The only sequence similarity between the GluRSs of these Bacillus species and the E. coli glutaminyl-tRNA synthetase (GlnRS), which has no counterpart in the E. coli GluRS, is in a segment of 30 amino acids in the last third of these synthetases. In the three-dimensional structure of the E. coli tRNA(Gln).GlnRS.ATP complex, this conserved peptide is near the anticodon of tRNA(Gln) (Rould, M. A., Perona, J. J., Söll, D., and Steitz, T. A. (1989) Science 246, 1135-1142), suggesting that this region is involved in the specific interactions between these enzymes and the anticodon regions of their tRNA substrates.

Amino Acid Sequence↗
PubMed1990

Precise mapping and comparison of two evolutionarily related regions of the Escherichia coli K-12 chromosome. Evolution of valU and lysT from an ancestral tRNA operon.

Two tRNA operons have been found near the gltX gene encoding the glutamyl-tRNA synthetase of Escherichia coli K-12. The alaW operon previously undetected from genetic data and containing two identical tRNA(GGCAla) genes is 800 base-pairs downstream from the gltX terminator and is transcribed from the same strand. The valU operon containing genes for three identical tRNA(UACVal) and one tRNA(UUULys) (the wild-type allele of supN), is adjacent to gltX and is transcribed from the opposite strand. Five open reading frames were also found in this region encoding putative polypeptides of 62, 105, 130, 167 and 294 amino acid residues. ORF294 is a new member of the lysR family of bacterial transcriptional activators. The possibility that this is the xapR gene is discussed. Comparison of the physical and linkage maps of the E. coli chromosome in the 52 minute region has permitted precise mapping of most of the 18 genes in this region with the order nupC-glk- less than (alaW beta-ala W alpha)-1 kb- less than gltX-0.3 kb-(valU alpha-valU beta-valU gamma-lysV = supN) greater than xapR-xapA- less than lig-1 kb-cysK greater than -0.4 kb-ptsH greater than -0.05 kb-pstI greater than -0.05 kb-crr greater than -cysM-cysA in the clockwise order (greater than and less than indicate the direction of transcription; kb, 10(3) bases). The last two genes of valU (52 min) and lysT (16.5 min) are arranged in a similar fashion and a highly conserved region has been found in both operons. This suggests that the valU and lysT operons probably arose by a duplication of an ancestral tRNA operon. This is the first example of what may be two different tRNA operons from the same organism evolving from an ancestral tRNA gene. Comparison of the 16 and 52 minute regions of the E. coli K-12 chromosome suggests that these two regions could share a common ancestor.

Amino Acid Sequence↗
PubMed1990

Closely spaced and divergent promoters for an aminoacyl-tRNA synthetase gene and a tRNA operon in Escherichia coli. Transcriptional and post-transcriptional regulation of gltX, valU and alaW.

The transcription of the gltX gene encoding the glutamyl-tRNA synthetase and of the adjacent valU and alaW tRNA operons of Escherichia coli K-12 has been studied. The alaW operon containing two tRNA(GGCAla) genes, is 800 base-pairs downstream from the gltX terminator and is transcribed from the same strand. The valU operon, containing three tRNA(UACVal) and one tRNA(UUULys) (the wild-type allele of supN) genes, is adjacent to gltX and is transcribed from the opposite strand. Its only promoter is upstream from the gltX promoters. The gltX gene transcript is monocistronic and its transcription initiates at three promoters, P1, P2 and P3. The transcripts from one or more of these promoters are processed by RNase E to generate two major species of gltX mRNA, which are stable and whose relative abundance varies with growth conditions. The stability of gltX mRNA decreases in an RNase E- strain and its level increases with growth rate about three times more than that of the glutamyl-tRNA synthetase. The 5' region of these mRNAs can adopt a stable secondary structure (close to the ribosome binding site) that is similar to the anticodon and part of the dihydroU stems and loops of tRNA(Glu), and which might be involved in translational regulation of GluRS synthesis. The gltX and valU promoters share the same AT-rich and bent upstream region, whose position coincides with the position of the upstream activating sequences of tRNA and rRNA promoters to which they are similar. This suggests that gltX and valU share transcriptional regulatory mechanisms.

Amino Acyl-tRNA Synthetases↗
PubMed1990

Superiority of dipyridamole over exercise testing when exercise thallium imaging is limited by angina.

The extent of jeopardized myocardium can be underestimated on stress thallium myocardial perfusion images when exercise tolerance is limited by angina pectoris. A patient's tolerance for pain can influence the degree of myocardial ischemia observed on myocardial perfusion images during effort angina. A case is reported of a patient with angina pectoris showing mild ischemia limited to one myocardial segment on exercise thallium images, but severe and extensive reversible perfusion defects during dipyridamole-thallium imaging, and a 70% stenosis of the left main coronary artery on coronary angiography.

Angina Pectoris↗
PubMed1989

Usefulness of the severity and extent of reversible perfusion defects during thallium-dipyridamole imaging for cardiac risk assessment before noncardiac surgery.

Thallium-dipyridamole imaging is a very sensitive test for predicting cardiac events after noncardiac surgery, but it lacks specificity. To improve specificity, a semiquantitative scoring system was developed that combined dipyridamole-induced reversible left ventricular dilatation with scintigraphic indexes for severity and extent of reversible perfusion defects. Using this scoring system, patients were classified into low, intermediate and high risk subgroups. Thallium-dipyridamole imaging was performed in 66 patients before major general and vascular surgery. Thirty-nine patients classified as low risk (30 with normal scans and 9 with fixed defects) underwent surgery uneventfully. Surgery was cancelled in 6 patients with extensive thallium redistribution and coronary angiography was performed because of severe coronary artery disease in 5 and idiopathic dilated cardiomyopathy in 1. In the remaining 21 patients with thallium redistribution, a positive statistical correlation (p = 0.001) between scintigraphic indexes of severity and extent, and cardiac events was noted. Using cutoff values for the scintigraphic indexes, patients with reversible defects could be classified into intermediate and high risk subgroups. Only 1 of 11 patients at intermediate risk developed a complication, whereas 8 of 10 patients at high risk had a postoperative event (7 deaths and 1 myocardial infarction). Thus, using scintigraphic indexes for severity and extent, patients with reversible defects can be stratified into an intermediate risk subgroup that can safely undergo surgery and a high risk subgroup that requires coronary angiography.

Angiography↗
PubMed1989

Cloning and sequencing of the gltX gene, encoding the glutamyl-tRNA synthetase of Rhizobium meliloti A2.

The gltX gene, coding for the glutamyl-tRNA synthetase of Rhizobium meliloti A2, was cloned by using as probe a synthetic oligonucleotide corresponding to the amino acid sequence of a segment of the glutamyl-tRNA synthetase. The codons chosen for this 42-mer were those most frequently used in a set of R. meliloti genes. DNA sequence analysis revealed an open reading frame of 484 codons, encoding a polypeptide of Mr 54,166 containing the amino acid sequences of an NH2-terminal and various internal fragments of the enzyme. Compared with the amino acid sequence of the glutamyl-tRNA synthetase of Escherichia coli, the N-terminal third of the R. meliloti enzyme was strongly conserved (52% identity); the second third was moderately conserved (38% identity) and included a few highly conserved segments, whereas no significant similarity was found in the C-terminal third. These results suggest that the C-terminal part of the protein is probably not involved in the recognition of substrates, a feature shared with other aminoacyl-tRNA synthetases.

Amino Acid Sequence↗
PubMed1989

Overproduction and domain structure of the glutamyl-tRNA synthetase of Escherichia coli.

The charging of glutamate on tRNA(Glu) is catalyzed by glutamyl-tRNA synthetase, a monomer of 53.8 kilodaltons in Escherichia coli. To obtain the large amounts of enzyme necessary for the identification of structural domains, we have inserted the structural gene gltX in the conditional runaway-replication plasmid pOU61, which led to a 350-fold overproduction of glutamyl-tRNA synthetase. Partial proteolysis of this enzyme revealed the existence of preferential sites of attack that, according to their N-terminal sequences, delimit regions of 12.9, 2.3, 12.1, and 26.5 kilodaltons from the N- to C-terminal of the enzyme. Their sizes suggest that the 2.3-kilodalton fragment is a hinge structure, and that those of 12.9, 12.1, and 26.5 kilodaltons are domain structures. The 12.9-kilodalton domain of the glutamyl-tRNA synthetase of E. coli is the only long region of this enzyme displaying a good amino acid sequence similarity with the glutaminyl-tRNA synthetase of Escherichia coli.

Amino Acid Sequence↗
PubMed1989

Purification and partial amino acid sequence of a glutamyl-tRNA synthetase from Rhizobium meliloti.

A glutamyl-tRNA synthetase has been purified to homogeneity from Rhizobium meliloti, using reversed-phase chromatography as the last step. Amino acid sequencing of the amino-terminal region of the enzyme indicates that it contains a single polypeptide, whose molecular weight is about 54,000, as judged by SDS-gel electrophoresis. The primary structures of the amino-terminus region and of an internal peptide obtained by cleavage of the enzyme with CNBr have similarities of 58 and 48% with regions of the glutamyl-tRNA synthase of Escherichia coli; these are thought to be involved in the binding of ATP and tRNA, respectively. The small amount of glutamyl-tRNA synthetase present in R. meliloti is consistent with the metabolic regulation of the biosynthesis of many aminoacyl-tRNA synthetases.

Amino Acid Sequence↗
PubMed1989

Transient mitral regurgitation: an adjunctive sign of myocardial ischemia during dipyridamole-thallium imaging.

A patient developed transient exacerbation of a mitral insufficiency murmur and a reversible posterior wall perfusion defect during dipyridamole-thallium imaging. Coronary angiography showed significant stenoses of both the right and the circumflex coronary arteries that supply the posterior papillary muscle. Cardiac auscultation for transient mitral incompetence, a sign of reversible papillary muscle dysfunction, is a simple and practical adjunctive test for myocardial ischemia during dipyridamole-thallium imaging. It may confirm that an isolated reversible posterior wall myocardial perfusion defect is truly ischemic in nature as opposed to an artifact resulting from attenuation by the diaphragm.

Aged↗
PubMed1988

Characterization of the Azorhizobium sesbaniae ORS571 genomic locus encoding NADPH-glutamate synthase.

Sixteen independent Azorhizobium sesbaniae ORS571 vector insertion (Vi) mutants defective in ammonium assimilation (Asm-) were selected; genomic DNA sequences flanking the insertion endpoints were cloned directly. Resulting recombinant plasmids were used to identify, by hybridization, corresponding wild-type DNA sequences from an A. sesbaniae lambda EMBL3 genomic library (lambda Asm phages). All 16 Asm- Vi mutants physically mapped to a single genomic locus. Plasmid subclones of recombinant phage lambda Asm152 were able to complement both Escherichia coli gltB and A. sesbaniae Asm- Vi mutants; NADPH-glutamate synthase activity was detected in all such strains complemented to Asm+. Heterologous and homologous complementations required both A. sesbaniae gltA+ and (inferred) gltB+ genes. Eleven A. sesbaniae Asm- Vi mutants mapped to a 4-kilobase-pair (kbp) DNA region that exhibited homology with Bacillus subtilis gltA+. In E. coli maxicell labeling experiments, this 4-kbp DNA region encoded a 165-kilodalton polypeptide that was inferred to be the product of the A. sesbaniae gltA+ gene (glutaminase NADPH-dependent L-glutamate synthase subunit). Site-directed Tn5-lacZ mutagenesis of a glt plasmid subclone identified a region that bisected this locus into (at least) two cistrons. Because the remaining five A. sesbaniae Asm- mutants mapped to a 1.5-kbp region adjacent to gltA+, these mutants probably define a single gltB+ gene (glutamate dehydrogenase NADPH-dependent L-glutamate synthase subunit); this region did not exhibit homology with the B. subtilis gltB+ gene.

Ammonia↗
PubMed1988

Pentylenetetrazole inhibits glutamate dehydrogenase and aspartate aminotransferase, and stimulates GABA aminotransferase in homogenates from rat cerebral cortex.

The mechanism by which pentylenetetrazole provokes convulsions in animals has been investigated by measuring its influence in vitro on the activities of several enzymes of glutamate metabolism in rat brain homogenates. Pentylenetetrazole does not affect the specific activities of glutamine synthetase, glutaminase, or glutamate decarboxylase; it inhibits those of glutamate dehydrogenase and aspartate aminotransferase, and stimulates that of gamma-aminobutyric acid (GABA) aminotransferase. The overall consequence of the action of pentylenetetrazole on the activities of these enzymes should be an increase in the concentration of glutamate and a decrease in that of GABA. This modulation of glutamate and GABA metabolism by pentylenetetrazole could contribute to the triggering of convulsions.

4-Aminobutyrate Transaminase↗