Homeless adolescents: a hidden crisis.
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Adolescent↗
Biomedical subjects
J M Robertson
Publications and source records attributed to J M Robertson.
Dieulafoy's lesion associated with truncus arteriosus type IV: an unusual cause of upper gastrointestinal hemorrhage.
Dieulafoy's lesion is an abnormal submucosal artery in the stomach characterized by massive and often fatal upper gastrointestinal hemorrhage. Diagnosis is usually made at operation, as endoscopy and arteriography frequently fail to identify the lesion. Embolization may be helpful, but surgery is generally the treatment of choice. We present the first reported case of Dieulafoy's lesion in a 17-yr-old boy with type IV truncus arteriosus. This congenital cardiac anomaly may have predisposed this patient to early manifestation of Dieulafoy's lesion, a rare and frequently unrecognized disorder.
Adolescent↗
Shielding of the D loop of ribosome-bound tRNA by elongation factor G.
The topography of the complex of elongation factor G with post-translocative ribosomes has been studied in the Escherichia coli system using fluorescence spectroscopy. We find that a fluorophore attached to the D loop of tRNA is shielded from solvent access by the presence of the factor, and this effect is dependent on factor-promoted GTP hydrolysis. The shielding result suggests that (1) the factor could bind to the tRNA during translocation and (2) the tRNA binding site may be close to that of the factor. The alternative explanation, that the factor affects the conformation of the tRNA bound at a distant site, seems less likely.
Escherichia coli↗
'Bilateral facial swelling in bulimia'.
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Bulimia↗
Mechanism of ribosomal translocation. tRNA binds transiently to an exit site before leaving the ribosome during translocation.
Escherichia coli ribosomes have a site (E) to which deacylated tRNA binds transiently before leaving the ribosome during translocation. The affinity of the site is Mg2+ dependent and low at physiological Mg2+ concentrations. Correct codon-anticodon interaction is unnecessary in this site. With these features, the E site cannot reduce frameshift errors through additional mRNA anchorage. Occupancy of the A site does not influence the tRNA binding in the E site, although a conformational change of elongation factor G, brought about by GTP hydrolysis, is necessary for efficient tRNA release. The tRNA can dissociate unhindered from the E site when the elongation factor is bound to the ribosome by fusidic acid. During elongation, the thermodynamically stable state is not attained, since E site occupation inhibits translocation. However, the E site can aid elongation by providing an intermediate state for tRNA dissociation, dispersing the process into more than one step.
Allosteric Site↗
A new technique for permanent pacemaker implantation in infants and children.
Permanent pacemaker implantation in the infant or young child presents the surgeon with many technical problems unique to this population. A new technique of implantation is described that was used successfully in 6 pediatric patients. The technique is simple to perform and gives very satisfactory results.
Child↗
Some calculations on the prevalence of dementia in Canada.
The epidemiology of dementia in Canada is not known. However, we report figures on the frequency of dementia in institutions in Ontario based upon the use of a multidimensional observation scale for the assessment of the elderly. These findings on institutionalized patients can be extrapolated to the whole elderly population, but the procedure is clearly too conservative by comparison with findings in other countries and in the light of the known occurrence of numbers of demented patients outside institutions. Ratios in different studies for the numbers of patients with dementia outside institutions and within institutions range from 1:1 to 6:1. Using a ratio of 2:1 and applying it to age specific population figures, a prevalence of dementia in Canada of 222,324 for those over 65 is obtained with a rate of 9.4% in that age group. When the figures projected in this way are compared with five epidemiological studies for the rate of dementia elsewhere, the Canadian figure which we have obtained ranks fourth out of six. This estimate provides potential figures on which to base the planning of services, provided that the inferential nature of the estimates is fully recognized.
Aged↗
Pre-steady-state kinetics of ribosomal translocation.
The two partial reactions of elongation factor G dependent translocation, the release of deacylated tRNA from the P site and the displacement of peptidyl tRNA from the A to the P site, have been studied with the stopped-flow technique. The experiments were performed with poly(U)-programmed ribosomes from Escherichia coli carrying deacylated tRNAPhe in the P site and N-AcPhe-tRNAPhe in the A site in the presence of GTP. The kinetics of the reaction were followed by monitoring either the intensity or the polarization of the fluorescence of both wybutine and proflavine located in the anticodon loop or of proflavine located in the D loop of yeast tRNAPhe or N-AcPhe-tRNAPhe. Both displacement and release fluorescence changes could be described by three exponentials, exhibiting apparent first-order rate-constants (20 degrees C) of 2 to 5 s-1 (15 s-1, 35 degrees C), 0.1 to 0.3 s-1, and 0.01 to 0.02 s-1, measured with a saturating concentration of elongation factor G (1 microM). The activation energy for the fast process of both reactions was found to be 70 kJ/mol (17 kcal/mol), while the intermediate process exhibits an activation energy of 30 kJ/mol (7 kcal/mol). The fast step is assigned to the displacement of the N-AcPhe-tRNAPhe from the A to the P site, and to the release of the tRNAPhe from the P site. The reactions take place simultaneously to form an intermediate post-translocation complex. The latter, in the intermediate step, rearranges to form a post-translocation complex carrying the deacylated tRNAPhe in an exit site and N-AcPhe-tRNAPhe in the P site, both in their equilibrium states. In parallel, or subsequently, the deacylated tRNAPhe spontaneously dissociates from the ribosome, thus completing the translocation process. The slow process has not been assigned.
Bacterial Proteins↗
Mechanism of ribosomal translocation. Translocation limits the rate of Escherichia coli elongation factor G-promoted GTP hydrolysis.
The pre-steady-state kinetics of GTP hydrolysis catalysed by elongation factor G and ribosomes from Escherichia coli has been investigated by the method of quenched-flow. The GTPase activities either uncoupled from or coupled to the ribosomal translocation process were characterized under various experimental conditions. A burst of GTP hydrolysis, with a kapp value greater than 30 s-1 (20 degrees C) was observed with poly(U)-programmed vacant ribosomes, either in the presence or absence of fusidic acid. The burst was followed by a slow GTP turnover reaction, which disappears in the presence of fusidic acid. E. coli tRNAPhe, but not N-acetylphenylalanyl-tRNAPhe (N-AcPhe-tRNAPhe), stimulates the GTPase when bound in the P site. If the A site of poly(U)-programmed ribosomes, carrying tRNAPhe in the P site, is occupied by N-AcPhe-tRNAPhe, the burst of Pi discharge is replaced by a slow GTP hydrolysis. Since, under these conditions, N-AcPhe-tRNAPhe is translocated from the A to the P site, this GTP hydrolysis very probably represents a GTPase coupled to the translocation reaction.
Escherichia coli↗
Affinities of tRNA binding sites of ribosomes from Escherichia coli.
The binding affinities of tRNAPhe, Phe-tRNAPhe, and N-AcPhe-tRNAPhe from either Escherichia coli or yeast to the P, A, and E sites of E. coli 70S ribosomes were determined at various ionic conditions. For the titrations, both equilibrium (fluorescence) and nonequilibrium (filtration) techniques were used. Site-specific rather than stoichiometric binding constants were determined by taking advantage of the varying affinities, stabilities, and specificities of the three binding sites. The P site of poly(U)-programmed ribosomes binds tRNAPhe and N-AcPhe-tRNAPhe with binding constants in the range of 10(8) M-1 and 5 X 10(9) M-1, respectively. Binding to the A site is 10-200 times weaker, depending on the Mg2+ concentration. Phe-tRNAPhe binds to the A site with a similar affinity. Coupling A site binding of Phe-tRNAPhe to GTP hydrolysis, by the addition of elongation factor Tu and GTP, leads to an apparent increase of the equilibrium constant by at least a factor of 10(4). Upon omission of poly(U), the affinity of the P site is lowered by 2-4 orders of magnitude, depending on the ionic conditions, while A site binding is not detectable anymore. The affinity of the E site, which specifically binds deacylated tRNAPhe, is comparable to that of the A site. In contrast to P and A sites, binding to the E site is labile and insensitive to changes of the ionic strength. Omission of the mRNA lowers the affinity at most by a factor of 4, suggesting that there is no efficient codon-anticodon interaction in the E site. On the basis of the equilibrium constants, the displacement step of translocation, to be exergonic, requires that the tRNA leaving the P site is bound to the E site. Under in vivo conditions, the functional role of transient binding of the leaving tRNA to the E site, or a related site, most likely is to enhance the rate of translocation.
Binding Sites↗
Separation methods in the estrogen-receptor assay: dextran-coated charcoal compared with glass fibre.
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Autoanalysis↗
Safety of prolonged aortic clamping with blood cardioplegia. III. Aspartate enrichment of glutamate-blood cardioplegia in energy-depleted hearts after ischemic and reperfusion injury.
This study tests the hypothesis that aspartate enrichment of glutamate-blood cardioplegia improves metabolic and functional recovery after ischemic and reperfusion damage. Ischemic and reperfusion damage were produced in 15 dogs by 45 minutes of aortic clamping at 37 degrees C and 5 minutes of blood reperfusion, before 2 more hours of aortic clamping (simulated operation). Six received multidose blood cardioplegia at 4 degrees C. In nine others, the cardioplegic solution was infused at 37 degrees C for the first 5 minutes, followed by multidose infusions at 4 degrees C. Four received 26 mmol glutamate-enriched cardioplegic solution. In five, the glutamate (13 mmol) cardioplegic solution was enriched with aspartate (13 mmol). Oxygen uptake and ventricular function (stroke work index, left atrial pressure) were measured. These data suggest aspartate enrichment produced the highest oxygen uptake (32 +/- 4 versus 17 +/- 2 ml/100 gm for glutamate and 7 +/- 1 ml/100 gm for 4 degrees C blood cardioplegia). Complete functional recovery occurred in aspartate/glutamate-treated hearts (stroke work index 90% +/- 4%, left atrial pressure 12 +/- 2 mm Hg), whereas recovery was incomplete with both glutamate alone (stroke work index 66% +/- 14%, left atrial pressure 20 +/- 3 mm Hg) and 4 degrees C blood cardioplegia at low cardiac outputs. Eight of 10 hearts not receiving aspartate failed at high cardiac outputs. Aspartate enrichment of glutamate-blood cardioplegia improves recovery after severe ischemic/reperfusion damage by improving oxidative metabolism during cardioplegic infusion and during postischemic work.
Animals↗
Mitral valve replacement complicated by unsuspected pheochromocytoma.
This report describes the case of a 65-year-old woman who underwent elective mitral valve replacement complicated by a malignantly vasoactive pheochromocytoma. The early recognition of this condition and the importance of immediate and aggressive pharmacologic intervention are discussed.
Adrenal Gland Neoplasms↗
Drought-induced increases in abscisic Acid levels in the root apex of sunflower.
Abscisic acid (ABA) levels in 3-mm apical root segments of slowly droughted sunflower plants (Helianthus annuus L. cv Russian Giant) were analyzed as the methyl ester by selected ion monitoring gas chromatography-mass spectrometry using characteristic ions. An internal standard, hexadeuterated ABA (d6ABA) was used for quantitative analysis. Sunflower seedlings, grown in aeroponic chambers, were slowly droughted over a 7-day period. Drought stress increased ABA levels in the root tips at 24, 72, and 168 hour sample times. Control plants had 57 to 106 nanograms per gram ABA dry weight in the root tips (leaf water potential, -0.35 to -0.42 megapascals). The greatest increase in ABA, about 20-fold, was found after 72 hours of drought (leaf water potential, -1.34 to -1.47 megapascals). Levels of ABA also increased (about 7- to 54-fold) in 3-mm apical root segments which were excised and then allowed to dessicate for 1 hour at room temperature.
Journal Article↗
Biodegradation of [14C]phenol in secondary sewage and landfill leachate measured by double-vial radiorespirometry.
Double-vial radiorespirometry was used to estimate the biodegradation rates of 14C-labeled phenol in a landfill leachate and a secondary treated domestic wastewater. Rates were found to be comparable for each material at each of the three concentrations tested. Sewage microorganisms immediately began biodegrading the [14C]phenol; landfill leachate microorganisms required a lag period before maximum biodegradation of the [14C]phenol. The apparent rate of [14C]phenol biodegradation was 2.4 times faster in the sewage than in the landfill leachate. Double-vial radiorespirometry was shown to be an effective method for screening biodegradation rates in aquifers.
Biodegradation, Environmental↗
tRNA binding sites of ribosomes from Escherichia coli.
70S tight-couple ribosomes from Escherichia coli were studied with respect to activity and number of tRNA binding sites. The nitrocellulose filtration and puromycin assays were used both in a direct manner and in the form of a competition binding assay, the latter allowing an unambiguous determination of the fraction of ribosomes being active in tRNA binding. It was found that, in the presence of poly(U), the active ribosomes bound two molecules of N-AcPhe-tRNAPhe, one in the P and the other in the A site, at Mg2+ concentrations between 6 and 20 mM. A third binding site in addition to P and A sites was observed for deacylated tRNAPhe. At Mg2+ concentrations of 10 mM and below, the occupancy of the additional site was very low. Dissociation of tRNA from this site was found to be rather fast, as compared to both P and A sites. These results suggest that the additional site during translocation functions as an exit site, to which deacylated tRNA is transiently bound before leaving the ribosome. Since tRNA binding to this site did not require the presence of poly(U), a function of exit site bound tRNA in the fixation of the mRNA appears unlikely. Both the affinity and stability of binding to the additional site were found lower for the heterologous tRNAPhe from yeast as compared to the homologous one. This difference possibly indicates some specificity of the E. coli ribosome for tRNAs from the same organism.
Binding Sites↗
Pericardiectomy: a changing scene.
The indications for pericardiectomy as well as the causal factors have changed in recent years. Sixty-eight patients operated on at the UCLA Medical Center between 1955 and 1982 have been described. There were 37 male patients and 31 female patients. The indication for operation was acute pericarditis in 37 patients, of whom 31 had recurrent effusion, and chronic constrictive pericarditis in 31 patients, of whom 8 were calcific. The most common cause of pericardial disease was tumor (20 patients), followed by idiopathic (13 patients), uremic (7 patients), viral (7 patients), tuberculous (6 patients), rheumatologic (6 patients), and miscellaneous (9 patients) causes. In most patients, pericardiectomy was performed through a left anterolateral thoracotomy without cardiopulmonary bypass. We recommend wide excision of the anterior pericardium (phrenic nerve to phrenic nerve) for effusive pericarditis. For chronic constrictive disease, we advocate a more extensive resection that includes the anterior as well as the posterior pericardium, thus freeing the left and right ventricles. Excellent long-term results were obtained with pericardiectomy in 90 percent of the patients who survived the operation.
Adolescent↗
Safety of prolonged aortic clamping with blood cardioplegia. I. Glutamate enrichment in normal hearts.
This study compares the protection provided by prolonged (4 hours) aortic clamping with glutamate-enriched potassium blood cardioplegia (n = 8) to (1) prolonged (4 hours) aortic clamping with multidose potassium blood cardioplegia without glutamate (n = 4), (2) 4 hours of continuous perfusion of the beating empty heart (n = 7), and (3) 15 minutes of normothermic ischemia (n = 10). According to measurements of myocardial oxygen uptake, left ventricular compliance, left ventricular contractility, and stroke work performance, no statistical difference could be detected between those hearts receiving blood cardioplegia either with or without glutamate enrichment. In both of these groups, myocardial protection was excellent, as demonstrated by the following: postischemic myocardial oxygen uptake 43% (p less than 0.05) above control, 95% +/- 6% recovery of the left ventricular compliance, a 97% +/- 5% return of the left ventricular contractility, and a 91% +/- 6% recovery of stroke work index. Contrary to the excellent recovery of those hearts receiving blood cardioplegic protection, those hearts undergoing 4 hours of continuous perfusion showed a 45% +/- 16% (p less than 0.05) loss of left ventricular compliance and a 72% +/- 8% (p less than 0.05) recovery of stroke work index; those hearts experiencing 15 minutes of normothermic ischemia showed a 74% +/- 6% (p less than 0.05) return of left ventricular compliance, a 30% +/- 5% (p less than 0.05) decrease in contractility, and a 56% +/- 5% (p less than 0.05) recovery of postischemic left ventricular stroke work.
Animals↗