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Biomedical subjects

J M Smith

Publications and source records attributed to J M Smith.

At least 289 records · Page 16Linked to original sources
PubMed1990

Quantitative analysis of one-dimensional gel electrophoresis profiles.

A general method for the one-dimensional quantitative analysis of band profiles from an autoradiographed or stained gel is described. Curved lanes may be tracked, noise across the width of the band reduced by local averaging of densities within a selected window, and background-corrected density profiles produced. Sections of each profile can be subjected to a choice of three methods of peak-area determination, depending on the type of gel and the requirements of the analysis being carried out. In the first method, simple integration is used to measure the area under the profile between any two positions. The second method integrates a Gaussian distribution fitted to a single peak. Where bands overlap, the third method resolves peaks into their component areas, taking into account the observed increase in the width of the band in the direction of electrophoretic migration. This is incorporated into a least-squares profile-fitting method, which is shown to be both accurate and efficient.

Electrophoresis↗
PubMed1990

Purification and characterization of D-2-haloacid dehalogenase from Pseudomonas putida strain AJ1/23.

A D-2-haloacid dehalogenase was isolated and purified to homogeneity from Pseudomonas putida strain AJ1/23. The enzyme catalysed the stereospecific dehalogenation of the D-isomer of 2-chloropropionate. Using a new ion-chromatograph assay, the enzyme was found to catalyse the dehalogenation of short-chain 2-halocarboxylic acids. Maximum enzyme activity occurred at pH 9.5 and 50 degrees C and the enzyme was insensitive to most -SH reagents. The enzyme has an Mr of about 135,000 and appears to be composed of four subunits of identical Mr.

Hydrocarbons, Chlorinated↗
PubMed1990

Purine biosynthesis in Escherichia coli K12: structure and DNA sequence studies of the purHD locus.

The de novo purine biosynthetic enzymes 5-amino-4-imidazolecarboxamide-ribonucleotide (AICAR) transformylase (EC 2.1.2.3), IMP cyclohydrolase (EC 3.5.4.10) and glycineamide-ribonucleotide (GAR) synthetase (EC 2.1.2.2) are encoded by the purHD locus of Escherichia coli. The DNA sequence of this locus revealed two open reading frames encoding polypeptides of Mr 57,335 and 45,945 (GAR synthetase), respectively, that formed an operon. The DNA sequence, maxicell and complementation analyses all supported the concept that the Mr 57,335 polypeptide is the product of the purH gene and encodes a bifunctional protein containing both AICAR transformylase and IMP cyclohydrolase activities. The 5' end of the purHD mRNA was determined by primer extension mapping and contains two regions of dyad symmetry capable of forming 'hairpin' loops where the formation of the one would prevent the formation of the other but not vice versa. Regulation by the purR gene product was explained by the discovery of a purR binding site in the purHD control region.

Acyltransferases↗
PubMed1990

Extracorporeal shockwave lithotripsy monotherapy for paediatric urinary tract calculi.

The role of extracorporeal shockwave lithotripsy (ESWL) in the management of paediatric urinary tract calculi was evaluated. The study group included 22 children (13 male, 9 female) with an age range of 2 to 13 years. The renal calculi, including staghorn and ureteric calculi, varied in size from 0.3 to 5 cm. Overall stone clearance at 3 months was 79% with a low incidence of complications (2 children required nephrostomy drainage for sepsis). ESWL is a non-invasive method of managing even complex stones in children of all ages, irrespective of size or position.

Adolescent↗
PubMed1990

DNA sequence of the purC gene encoding 5'-phosphoribosyl-5-aminoimidazole-4-N-succinocarboxamide synthetase and organization of the dapA-purC region of Escherichia coli K-12.

5'-Phosphoribosyl-5-aminoimidazole-4-N-succinocarboxamide synthetase (EC 6.3.2.6), encoded by the purC gene of Escherichia coli K-12, catalyzes the synthesis of 5'-phosphoribosyl-5-aminoimidazole-4-N-succinocarboxamide from 5'-phosphoribosyl-5-aminoimidazole-4-carboxylic acid. The mature protein, as deduced from the purC structural gene sequence, contains 237 amino acids and has a calculated Mr of 26,998. The control region of the purC gene was identified by primer extension mapping of the 5' end of the purC mRNA. The purC control region contains a binding site for and is regulated by the purine repressor, the product of the purR gene. An unusual feature of the 5' untranslated region of the purC mRNA is the presence of a repetitive extragenic palindrome sequence normally found in intercistronic or 3' untranslated regions. The DNA sequence was extended 1.281 kilobases upstream of the purC structural gene and overlapped with the previously determined dapA sequence. Termination of transcription from the dapA-purC intercistronic region may occur within the -35 region of the purC control region. The purC gene has been positioned on the E. coli restriction map and is transcribed in a counterclockwise direction.

Amino Acid Sequence↗
PubMed1990

Genes of the Escherichia coli pur regulon are negatively controlled by a repressor-operator interaction.

Fusions of lacZ were constructed to genes in each of the loci involved in de novo synthesis of IMP. The expression of each pur-lacZ fusion was determined in isogenic purR and purR+ strains. These measurements indicated 5- to 17-fold coregulation of genes purF, purHD, purC, purMN, purL, and purEK and thus confirm the existence of a pur regulon. Gene purB, which encodes an enzyme involved in synthesis of IMP and in the AMP branch of the pathway, was not regulated by purR. Each locus of the pur regulon contains a 16-base-pair conserved operator sequence that overlaps with the promoter. The purR product, purine repressor, was shown to bind specifically to each operator. Thus, binding of repressor to each operator of pur regulon genes negatively coregulates expression.

Base Sequence↗
PubMed1990

Calcium antagonists inhibit elevated potassium efflux from aorta of aldosterone-salt hypertensive rats.

The purpose of this study was to evaluate the effect of calcium antagonists on basal tension and the elevated 42K efflux in aorta from aldosterone-salt hypertensive rats. Diltiazem decreased the basal tension (2.0 +/- 0.4 g) as well as the phasic contractile activity and returned the elevated 42K efflux (0.018 +/- 0.002/min) toward control values (0.010 +/- 0.001/min, p less than 0.001). The diltiazem median inhibitory concentration (IC50) for basal tension (0.04 +/- 0.02 microM), however, was sevenfold less than the IC50 for basal 42K efflux (0.22 +/- 0.08 microM, p less than 0.01). The basal 45Ca influx in aorta from aldosterone-salt hypertensive rats (120 +/- 4 microM/l cell H2O/min) was also decreased by diltiazem in a concentration-dependent manner, whereas the 45Ca influx in aorta from control-salt rats (135 +/- 3 microM/l cell H2O/min) was not altered. Similarly, the dihydropyridine nisoldipine eliminated the basal tension (2.7 +/- 0.5 g) and returned the elevated basal 42K efflux from the hypertensive aorta toward control levels (0.010 +/- 0.0003/min, p less than 0.001). The nisoldipine IC50 for basal tension (0.016 +/- 0.01 nM) was 160-fold less than the IC50 for basal 42K efflux (1.8 +/- 1.2 nm, p less than 0.001). Neither diltiazem nor nisoldipine nisoldipine altered the basal 42K efflux or contractile activity of aorta from control-salt rats. These results suggest that the basal tension and elevated 42K efflux in aorta from aldosterone-salt hypertensive rats are supported by the entry of extracellular calcium into the tissue through potential-operated calcium channels.

Aldosterone↗
PubMed1990

Development of a heating device for sampling arterialized venous blood from a hand vein.

A practical and safe heating device for sampling arterialized venous blood from a hand vein was constructed and tested under experimental conditions. Blood chemistry values (pH, pCO2, pO2 and O2 saturation) were measured in nine individuals from blood sampled from an antecubital vein and a hand vein, as well as from a hand vein that had been heated in the handwarmer. Only blood sampled from the heated hand vein gave blood gas values that were consistently in the arterial range. Mean blood gas values were 38.0 +/- 2.5 mmHg, 79.8 +/- 6.8 mmHg and 95.7 +/- 0.9% for pCO2, pO2 and O2 saturation, respectively, for blood sampled from the heated hand vein. No significant difference (P greater than 0.05) was evident in blood gas values whether blood was sampled 15, 30, 45, 60, 75 or 90 min after placing the hand in the heated handwarmer. The handwarmer enables arterialized venous blood sampling after 15 min of warming and is safe to use in any experimental or clinical situation where sampling from an artery is impractical.

Adult↗
PubMed1989

Glutathione redox state, lipid peroxide levels, and activities of glutathione enzymes in oltipraz-treated adult Schistosoma mansoni.

A decrease in reduced glutathione (GSH) levels in adult Schistosoma mansoni exposed in vitro to the antischistosomal drug oltipraz (OPZ) (20-60 nM) was accompanied by a significant increase in oxidized glutathione (GSSG) levels. The total glutathione (GSH + GSSG) levels also diminished in drug-treated parasites. The activities of the parasite glutathione peroxidase (GPO), utilizing cumene hydroperoxide as a substrate, and glutathione S-transferase (GST), measured 18 hr after in vitro incubation with the drug, were elevated significantly, but there were no significant alterations in the activities of the GPO, utilizing H2O2, or glutathione reductase (GR). Drug-treated worms showed increased lipid peroxidation. In vivo, the proportion of the worms recovered from infected mice given OPZ (100 mg/kg body wt) gradually declined with time, to about 30% of that recovered from infected untreated control mice by day 14 after drug administration, and consisted predominantly of male worms. Accompanying this significant decline in the proportion of worms recovered were significant decreases in the activities of the enzymes GR and GST in drug-exposed worms. On the other hand, a slight initial increase in the GPO activity with cumene hydroperoxide was followed by a return to control values, and the GPO activity with H2O2 was decreased only slightly with time. Interestingly, the 4-hydroxyalk-2-enal aldehydes, known products of lipid peroxidation, inhibited the GST reaction with 1-chloro-2,4-dinitrobenzene (CDNB). The OPZ-induced changes in S. mansoni could increase parasite susceptibility to oxidative attack by host phagocytes, and are probably linked with the antischistosomal action of the drug in vivo.

Animals↗
PubMed1989

The causes of extinction.

A species may go extinct either because it is unable to evolve rapidly enough to meet changing circumstances, or because its niche disappears and no capacity for rapid evolution could have saved it. Although recent extinctions can usually be interpreted as resulting from niche disappearance, the taxonomic distribution of parthenogens suggests that inability to evolve may also be important. A second distinction is between physical and biotic causes of extinction. Fossil evidence for constant taxonomic diversity, combined with species turnover, implies that biotic factors have been important. A similar conclusion emerges from studies of recent introductions of predators, competitors and parasites into new areas. The term 'species selection' should be confined to cases in which the outcome of selection is determined by properties of the population as a whole, rather than of individuals. The process has been of only trivial importance in producing complex adaptations, but of major importance in determining the distribution of different types of organisms. An adequate interpretation of the fossil record requires a theory of the coevolution of many interacting species. Such a theory is at present lacking, but various approaches to it are discussed.

Animals↗
PubMed1989

Beat to beat variability in cardiovascular variables: noise or music?

Cardiovascular variables such as heart rate, arterial blood pressure, stroke volume and the shape of electrocardiographic complexes all fluctuate on a beat to beat basis. These fluctuations have traditionally been ignored or, at best, treated as noise to be averaged out. The variability in cardiovascular signals reflects the homeodynamic interplay between perturbations to cardiovascular function and the dynamic response of the cardiovascular regulatory systems. Modern signal processing techniques provide a means of analyzing beat to beat fluctuations in cardiovascular signals, so as to permit a quantitative, noninvasive or minimally invasive method of assessing closed loop hemodynamic regulation and cardiac electrical stability. This method promises to provide a new approach to the clinical diagnosis and management of alterations in cardiovascular regulation and stability.

Cardiovascular Physiological Phenomena↗