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Biomedical subjects

G Bell

Publications and source records attributed to G Bell.

At least 145 records · Page 8Linked to original sources
PubMed1981

Interactions of low density lipoprotein receptors with coated pits on human fibroblasts: estimate of the forward rate constant and comparison with the diffusion limit.

We present a theoretical study of the interaction of low density lipoprotein (LDL) receptors with coated pits. From published experiments we estimate that the forward rate constant, k+, for the binding of a LDL receptor to a coated pit on a human fibroblast at 37 degrees C is greater than or equal to 3 X 10(-10) cm2/sec, and the mean time an LDL receptor spends on the cell surface before being captured by a coated pit, tc, is less than or equal to 1.8 min. If, when an LDL receptor enters, it remains within the coated pit until the coated pit pinches off to form a coated vesicle, then k+ = 3 X 10(-10) cm2/sec and tc = 1.8 min. We derive expressions for the diffusion limit of k+ and tc when particles (LDL receptors) diffuse in two dimensions until they hit and are absorbed by circular absorbers (coated pits) that have finite lifetimes. The absorbers appear and disappear at equal rates so that their concentration remains constant. We use these expressions to show that a diffusion limit of k+ = 3 X 10(-10) cm2/ sec would be obtained if D, the diffusion coefficient for an LDL receptor on a human fibroblast at 37 degrees C equaled 3.3 X 10(-11) cm2/sec. Because this value is in agreement with the experimentally determined value for D, we conclude that random insertion of LDL receptors into the plasma membrane, followed by pure diffusional motion of LDL receptors on the cell surface until they are irreversibly absorbed in coated pits, is consistent with experiment.

Cell Membrane↗
PubMed1981

Effect of oral salbutamol and slow-release aminophylline on exercise tolerance in chronic bronchitis.

In a double-blind placebo-controlled trial in 24 patients fulfilling the MRC criteria for chronic bronchitis, oral salbutamol 4 mg and slow-release aminophylline (Phyllocontin) 450 mg produced similar and significant (p less than 0.05) mean increases in forced expiratory volume in one second (FEV1). A significantly greater increase in mean FEV1 and forced vital capacity (FVC) was seen when both drugs were given although there was no statistical evidence of synergistic interaction. Salbutamol significantly increased the mean distance walked in 12 minutes (12MD) (p less than 0.02) by 56 metres and a similar increase of 54 metres (p less than 0.001) was seen after Phyllocontin. With both drugs in combination mean 12MD increased by 51 metres (p less than 0.02 cf placebo), a change not significantly different from that observed with either drug alone. Oral salbutamol and Phyllocontin improve exercise tolerance in chronic bronchitis. The significantly greater changes in FEV1 and FVC resulting from simultaneous administration of the two drugs are not associated with further improvement in exercise tolerance.

Adult↗
PubMed1980

Hospital variations in metastatic breast cancer.

Data from the tumor abstracts of 25,535 female breast cancer patients in California were analyzed to measure hospital differences in the rates of metastatic disease at diagnosis. For white patients the metastatic rates varied from 38 to 68 per cent as hospital affiliation varied, and for blacks they ranged from 48 to 76 per cent. Tests for normality showed that the distribution of rates for white patients in private facilities was not merely due to random variation. The metastatic rates for both racial groups tended to be inversely related to the proportion of whites among the patient populations and positively related to total patient load. Hospitals affiliated with medical schools had relatively high rates for white private patients. Several explanations of the data are suggested. They consider the possible effects of patient and physician health care practices and host vulnerability to the spread of breast cancer.

Black or African American↗
PubMed1979

Isolation and characterization of a cloned rat insulin gene.

The two nonallelic genes, insulin I and II of the rat, are separated by at least 7 kb of DNA. There is no obvious similarity in the sequence organization surrounding each gene, although the coding regions of the genes themselves share extensive homology. In three strains of rat, the insulin II gene lies predominantly on a 4.0 kb Eco RI restriction fragment, whereas the insulin I gene is located on a 9.4 kb Eco RI fragment in the Hooded strain, on a 7.2 kb Eco RI fragment in the Osborne-Mendel strain, and on both a 9.4 and a 7.2 kb Eco RI fragment in Sprague-Dawley rats. The 9.4 kb Eco RI fragment from Hooded rat DNA was isolated using the lambda cloning system, and the nucleotide sequence of this isolated rat insulin I gene and adjacent regions was determined. A translation in one frame of the sequence of the cloned gene confirms the protein sequence determined for rat pre-proinsulin I. The coding region of this gene lacks intervening sequences, although a presumptive intervening sequence of 119 bp is located in the 5 untranslated region preceding the prehormone sequence. The junctions around the 119 bp segment are identical to those which flank intervening sequences of other eucaryotic genes, AGGT. The site of polyadenylation was determined by direct sequence comparison with rat insulin cDNA clones, and a potential 5 "capping" site is proposed. A DNA sequence preceding this 5 "capping" site in the rat insulin I gene, TATAAAGC, is homologous to corresponding regions in other eucaryotic genes that have been proposed as putative promoter sites for the initiation of transcription.

Animals↗
PubMed1979

Direct determination of the properties of peptide transport systems in Escherichia coli, using a fluorescent-labeling procedure.

A direct study of peptide uptake by Escherichia coli was made using a fluorescent procedure. After incubation with the bacteria, peptides remaining in the medium were dansylated, separated chromatographically, and quantitated from their fluorescent intensities and/or from their incorporated radioactivity when tritiated dansyl derivatives were prepared. Peptide uptake was apparently not regulated and proceeded continuously until complete, with the absorbed peptides undergoing rapid intracellular hydrolysis and the excess amino acid residues leaving the cell. Thus, peptide uptake and amino acid exodus occur concurrently. However, peptidase-resistant substrates, e.g. triornithine and glycylsarcosine, which can be similarly estimated in cell extracts, were accumulated about 1,000-fold. The influence of amino acid composition and chain length on rates of transport was assessed. Different strains of E. coli showed variability in their rates of di- and oligopeptide transport. With respect to energy coupling, both the di- and oligopeptide permeases behaved like shock-sensitive transport systems.

Amino Acids↗
PubMed1979

Production and fate of erythroid cells in anaemic Xenopus laevis.

Adult Xenopus laevis, rendered anaemic by phenylhydrazine injection, have been studied during the recovery from such anaemia. Electron microscopy of liver and spleen sections indicates that both of these organs are active in the phagocytosis and destruction of the old damaged red blood cells. May-Grunwald and Giemsa staining of liver and spleen cells following anaemia has been used to show that erythropoiesis also occurs in both liver and spleen, and this has been confirmed by electron-microscope studies of these organs. Cell counting and radiolabelling of the new population of circulating erythroid cells in the period following phenylhydrazine injection suggests that a sudden release of basophilic erythroblasts from liver and spleen is followed by mitosis of this new cell population in circulation, and that no further release of erythroid cells from these organs is likely until complete recovery has occurred.

Anemia↗
PubMed1978

Comparison of a commercial identification kit and conventional biochemical tests used for the identification of enteric gram-negative rods.

A comparison between 11 Minitek biochemical tests and corresponding conventional tubed media was undertaken with 1,089 isolates of enteric gram-negative rods. Overall correlation between Minitek and conventional biochemicals was 97.4%. Minitek proved to be a time- and space-saving miniaturized biochemical system that can be used effectively for the identification of enteric gram-negative rods.

Bacteriological Techniques↗
PubMed1977

Thymidine-dependent strain of Salmonella oslo selected by trimethoprim-sulfamethoxazole therapy.

A case report describing the isolation of a multiple-drug-resistant strain of Salmonella oslo from urine and stool specimens is presented. After ten days of trimethoprim-sulfamethoxazole therapy, a second strain of Salmonella oslo was isolated from another stool specimen. The second strain was determined to be a thymidine-requiring organism. The significance of this thymidine-requiring strain is described.

Adult↗
PubMed1977

Monitoring enzyme synthesis as a means of studying peptide transport and utilization in Escherichia coli.

A new method has been developed for measuring peptide transport in aminoacid auxotrophs of Escherichia coli by following induction of beta-galactosidase. Appearance of the enzyme was determined after addition of inducer and peptides to amino-acid starved bacteria. For a given number of lysine equivalents, the rate and the extent of enzyme synthesis were the same for lysine and lysyl peptides; similar results were found for glycine and glycl peptides. Saturation constants for peptide transport were determined from the exogenous peptide concentration that gave half maximal rates of enzyme synthesis. The saturation constants, studies with mutants defective in peptide transport, and detection of competition between peptides for uptake, all endorsed earlier conclusions from growth tests about the structural specificities for peptide transport. The new method is quicker, more sensitive and more informative than growth tests.

Biological Transport↗
PubMed1976

Yeast DNA-dependent RNA polymerase I. A rapid procedure for the large scale purification of homogeneous enzyme.

A procedure has been developed for the rapid purification of large amounts of yeast RNA polymerase I (A). The method involves batchwise treatment with phosphocellulose and DEAE-cellulose, ion filtration chromatography on DEAE-Sephadex, sucrose gradient centrifugation, and DNA-cellulose chromatography. The enzyme obtained is apparently homogeneous by sedimentation velocity analysis and has a specific activity of 300 nmol of UMP incorporated into RNA in 10 min per mg of protein. Between 30 and 45 mg of enzyme can be obtained in 5 days from 3.0 kg of yeast cells. The subunit composition of the enzyme was determined by polyacrylamide gel electrophoresis in the presence of 0.1% sodium dodecyl sulfate. The purified polymerase is composed of 11 putative subunits with molecular weights 185,000 (Ia), 137,000 (Ib), 48,000 (Ic), 44,000 (Id), 41,000 (Ie), 36,000 (If), 28,000 (Ig), 24,000 (Ih), 20,000 (Ii), 14,500 (Ij), and 12,000 (Ik). Yeast polymerase I separates into two forms when subjected to gel electrophoresis under nondenaturing conditions. The main component which migrates faster contains all the subunits except the polypeptides Ic and If. The slow migrating component which is present in lower amounts contains all the subunits.

DNA-Directed RNA Polymerases↗
PubMed1976

Radioactive technetium phosphate bone scanning in preoperative assessment and follow-up study of patients with primary cancer of the breast.

Seventy-five female patients with early primary cancer of the breast were studied by bone scanning with 99mTc labeled phosphate at the time of initial presentation and serially during follow-up examination. Eleven patients had an abnormal bone scan at the time of presentation. During follow-up periods, which have ranged from three to 34 months with a mean of 16 months, abnormal bone scans have developed in a further 13 patients. To date, nine of the 24 patients with an abnormal bone scan have died, while only one of the 51 with a persistently normal scan has died. It is concluded that an abnormal bone scan carries a significant risk of earlier death due to metastatic disease.

Adult↗