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Biomedical subjects

J Burke

Publications and source records attributed to J Burke.

At least 163 records · Page 9Linked to original sources
PubMed1982

Structure and organization of tRNA, rRNA, and protein genes in neurospora crassa mitochondria.

Our studies on Neurospora crassa mitochondria have included sequence analysis of tRNAs, mapping and cloning of the tRNA, rRNA, and protein genes and the DNA sequence analysis of these genes. Results from tRNA sequence analyses explain how the mitochondrial protein synthesizing system can function with a much smaller number of tRNAs than other systems. Mapping studies have shown that the two rRNA genes and almost all of the tRNA genes are clustered onto a third of the mitochondrial genome. The two rRNA genes and all of the tRNA genes are coded for by the same DNA strand. DNA sequence analysis has provided several interesting results. Twenty-four tRNA genes have been identified. Highly conserved GC rich palindromic sequences flank tRNA genes. The intervening sequence within the large rRNA gene has a long open reading frame capable of coding for a protein 426 amino acids long. The gene for cytochrome oxidase subunit 3 has been localized within the tRNA-rRNA gene cluster and has been sequenced. This gene is also flanked by the highly conserved GC rich palindromic DNA sequences.

Amino Acid Sequence↗
PubMed1981

Glycoprotein biosynthesis in animal cells grown in suspension culture. Assembly of lipid-linked saccharides and formation of protein-bound 'high-mannose' oligosaccharides.

Glycoprotein biosynthesis was studied with mouse L-cells grown in suspension culture. Glucose-deprived cells incorporated [3H]mannose into 'high-mannose' protein-bound oligosaccharides and a few relatively high-molecular-weight lipid-linked oligosaccharides. The latter were retained by DEAE-cellulose and turned over quite slowly during pulse--chase experiments. Increased heterogeneity in size of lipid-linked oligosaccharides developed during prolonged glucose deprivation. Sequential elongation of lipid-linked oligosaccharides was also observed, and conditions that prevented the assembly of the higher lipid-linked oligosaccharides also prevented the formation of the larger protein-bound 'high-mannose' oligosaccharides. In parallel experiments, [3H]mannose was incorporated into a total polyribosome fraction, suggesting that mannose residues were transferred co-translationally to nascent protein. Membrane preparations from these cells catalysed the assembly from UDP-N-acetyl-D-[6-3H]glucosamine and GDP-D-[U-14C]mannose of polyisoprenyl diphosphate derivatives whose oligosaccharide moieties were heterogeneous in size. Elongation of the N-acetyl-D-[6-3H]glucosamine-initiated glycolipids with mannose residues produced several higher lipid-linked oligosaccharides similar to those seen during glucose deprivation in vivo. Glucosylation of these mannose-containing oligosaccharides from UDP-D-[6-3H]glucose was restricted to those of a relatively high molecular weight. Protein-bound saccharides formed in vitro were mainly smaller in size than those assembled on the lipid acceptors. These results support the involvement of lipid-linked saccharides in the synthesis of asparagine-linked glycoproteins, but show both in vivo and in vitro that protein-bound 'high-mannose' oligosaccharide formation can occur independently of higher lipid-linked oligosaccharide synthesis.

Animals↗
PubMed1981

Simplified estimation of glomerular filtration rate and effective renal plasma flow.

A method is described for the determination of GFR and ERPF using a combined injection of 51Cr-EDTA and 125I-iodohippurate. Plasma samples obtained at 60 min and 150 min after administration were used to determine a flow rate F assuming a monoexponential clearance of the tracers. Empirical relationships were found between F and the true GFR and ERPF determined from multiple sampling and multi-exponential analysis of the clearance curves. The method was shown to be superior to previously published methods involving one or two samples. GFR was calculated with a standard deviation (SD) of only 3.3 ml/min when compared to the multiple sample technique (the reference method), whereas the best estimate from a single sample had a SD of 6.3 ml/min. An improvement in accuracy of ERPF estimation was achieved for values of flow of less than 200 ml/min when the SD was only 9.3 ml/min.

Chromium Radioisotopes↗
PubMed1981

Comparison of larval antigens in an enzyme-linked immunosorbent assay for strongyloidiasis in humans.

An enzyme-linked immunosorbent assay for specific antibodies in patients with strongyloidiasis was developed using antigens extracted from the third-stage larvae of Strongyloides stercoralis and Strongyloides ratti. Sera from two groups of patients with strongyloidiasis proven by parasitologic methods, including one group of 29 coded positive sera, and from presumed normal subjects as controls were tested. Sera with optical density values greater than two standard deviations above the mean optical density value for the sera from control subjects were considered to be positive. Using this criterion 82%-84% of 51 positive patients had antibodies to S. stercoralis or S. ratti antigens. Immunosuppression and other factors that might influence antibody responses were associated with some patients who were negative for antibodies to Strongyloides. Antigen from an intestinal nematode of rats, Nippostrongylus brasiliensis, was also evaluated and found to be unsuitable for serodiagnosis of strongyloidiasis because of frequent false-positive as well as false-negative results.

Adult↗
PubMed1981

Bound Ribosomes of Pea Chloroplast Thylakoid Membranes: Location and Release in Vitro by High Salt, Puromycin, and RNase.

The mode of attachment of 70S ribosomes to thylakoid membranes from pea leaves was studied by determining the proportion of the bound RNA which was released by various incubation conditions. The results supported a model in which several classes of bound ribosomes could be distinguished: (a) very tightly bound, not released by any conditions yet tested (20% of the total); (b) monomeric ribosomes attached by electrostatic interaction with the membranes (30 to 40% of the total) and released by high salt; and (c) polysomes, with some of the ribosomes attached by a combination of electrostatic interactions and insertion of the nascent polypeptide chain into the membrane. These required a combination of puromycin and high salt for release. Other ("hanging") ribosomes of the polysomes were inferred to be attached through mRNA but not actually attached to the membranes directly; they could be released by RNase under low salt conditions, as well as by puromycin plus high salt.To obtain these results, chloroplasts had to be prepared in media containing 0.2 molar Tris at pH 8.5. Using Tricine buffers at pH 7.5 yielded thylakoid membranes whose ribosomes were removed almost completely by high salt alone; these showed no response to puromycin. However, pH 7.5 had to be used in all cases for ribosome dissociation in high salt media, as the ribosome structure appeared to be degraded by high salt at pH 8.5, and release then occurred without the need for puromycin.The kinetics of ribosome release by high salt showed a rapid initial phase with a half-life of 20 seconds. The extent of release by high salt was very dependent on the temperature of the incubation. Plotting the data according to the Arrhenius interpretation shows a significant break at about 15 C, with apparent activation energy of 20 kilocalories per mole below that temperature and 5 kilocalories per mole above that temperature. This result suggests that membrane fluidity might be an important factor permitting release of ribosomes under high salt conditions.Electron microscope pictures of the washed thylakoids showed polysomes closely associated with the outer membranes of grana stacks, and with the stroma lamellae. Following digitonin treatment of the membranes and centrifugation, fractions enriched in Photosystem I and presumed stroma lamellae were also enriched in bound RNA.

Journal Article↗
PubMed1981

Body composition in children on regular hemodialysis.

Body composition was estimated in 12 pubertal and 7 pre-pubertal children (age range 7-17 years) on regular hemodialysis for chronic renal failure (CRF). The results were expressed as a ratio of observed/predicted. Total body water (TBW) was normal and extracellular water (ECW) was significantly increased in both groups. Intracellular water (ICW), which reflects body cell mass, was significantly decreased in the pre-pubertal children but not in the pubertal children. The deviation in ICW from predicted normal was significantly more marked in the prepubertal children compared with pubertal children. Similarly, fat-free solids (FFS) were significantly decreased in the pre-pubertal, but normal in the pubertal children. Total body fat, estimated from body water, correlated significantly with skinfold thickness measurements and was normal in both groups, with the pre-pubertal children having significantly higher body fat ratio than pubertal children. Body fat was increased in some of the patients whose body cell mass was decreased. It is suggested that these changes are the result of a failure of normal energy metabolism with consequent body protein depletion, and that energy supplements as carbohydrate, particularly in the pre-pubertal patients, will increase body fat without affecting cell mass.

Adolescent↗
PubMed1980

The effects of anabolic steroids on growth, body composition, and metabolism in boys with chronic renal failure on regular hemodialysis.

Eight boys aged 9.5 to 17 years, on regular hemodialysis for chronic renal failure, were treated for 0.4 to 1.3 years with the anabolic steroid oxandrolone. The effects on linear growth, skeletal maturation, cell mass, and the fasting levels and response to intravenous glucose of BG, IRI, NEFA, BCAA, and IRG were measured. Following treatment there was a significant increase in mean growth velocity, growth velocity standard deviation score related to bone age, and cell mass. Overall skeletal maturation was not accelerated, and only a small advance in pubertal status was seen. There was a decrease in fasting levels of BG and NEFA; fasting BCAA and IRG were increased. The response to intravenous glucose was altered; there was a decrease in peak BG response, an increase in peak IRI response, and a more marked fall in plasma NEFA and BCAA levels. Fasting IRG levels correlated with fasting BG levels, and fell significantly following intravenous glucose both before and after treatment. Hepatotoxicity, which was reversible, was seen in a ninth boy who did not complete the study. The only other side effect, salt and water retention, was controlled by a reduction in oxandrolone dosage. These preliminary results suggest that anabolic steroids may be useful to stimulate anabolism and growth in uremic children, and that their effect is mediated by an increase in insulin secretion and/or an improvement in tissue sensitivity to insulin. Further studies with careful monitoring are required to substantiate the effect on final height and the risks involved.

Adolescent↗
PubMed1979

The assembly of lipid-linked oligosaccharides in plant and animal membranes.

Membrane preparations from growing regions of pea stems and actively-dividing mouse L-cells form lipid-linked saccharides from GDP-mannose and UDP-N-acetylglucosamine. These lipids have properties which are consistent with those of mono- and di-phosphoryl polyisoprenyl derivatives. In experiments using plant membranes, the monophosphoryl derivative labeled with GDP-(14C) mannose contains mannose only, while the diphosphoryl derivative labeled with the same nucleotide sugar is heterogeneous, containing oligosaccharides corresponding to mannosaccharides of 5, 7, and 9--12 residues. Only the diphosphoryl polyisoprenyl derivatives are labeled with UDP-(14C)glucosamine and these contain predominantly chitobiose and N-acetylglucosamine itself. Unlabeled GDP-mannose added after UDP-N-acetyl-(14C)glucosamine results in the formation of higher lipid-linked oligosaccharides which are apparently the same as those which are labeled with GDP-(14C)mannose alone. Incubation of the membranes with GDP-(14C)mannose in the presence of Mn2+, unlabeled UDP-glucose or unlabeled UDP-N-acetylglucosamine results in marked changes in the accumulation of both the polyisoprenyl monophosphoryl mannose and polyisoprenyl diphosphoryl oligosaccharides. Animal cell membranes synthesise lipid-linked oligosaccharides when incubated with UDP-N-acetylglucosamine and GDP-mannose. These oligosaccharides are similar in size to those synthesised by the plant membranes but their formation is more efficient. The potential roles of these compounds in glycoprotein biosynthesis in both plant and animal tissues is discussed.

Glycoproteins↗
PubMed1979

The management of fractures in Paget's disease of bone.

The results of the treatment of 89 fractures of bone affected by Paget's disease are presented. The typical features of these fractures, the common sites affected, the rate of healing and the complications involved, including the incidence of malignant change, are reviewed. The possible role of calcitonin in the prevention of these fractures is discussed.

Aged↗
PubMed1979

Effect of a group perceptual-motor training program on kindergarten children.

For 21 boys and 24 girls in a middle-class kindergarten no differences in Identification of Body Parts, Copy Forms, or Motor Skills Test of the Rosner-Richman Perceptual Survey were noted. Scores increased from September to May testing on copying and motor skills, e.g., walking a rail, balancing, handling balls, as expected.

Child Development↗
PubMed1976

The effects of stimulability on the articulation of /s/ relative to cluster and word frequency of occurrence.

This study investigated the effects of stimulability on the articulation of cluster nested /s/ in high- and low-frequency clusters and words. A good stimulability group and a poor stimulability group of /s/-defective seven-year-old children were investigated. Statistical analysis did not reveal significant differences between the articulatory performances of the two groups on words or clusters occurring with high or low frequency. Subjects in the good stimulability group obtained significantly fewer errors on the test stimuli than did subjects in the poor stimulability group. Correlational analyses indicated that stimulability was positively correlated with correct numbers of /s/ productions in both clusters and words occurring with both high and low frequency. Subjects' spontaneous /s/ errors on the Templin-Darley screening test were not found to be correlated with their stimulability scores or their imitative /s/ productions in words and clusters occurring with high or low frequencies.

Acoustic Stimulation↗