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G Smith

Publications and source records attributed to G Smith.

At least 361 records · Page 20Linked to original sources
PubMed1996

Noise? What noise?

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Ear Protective Devices↗
PubMed1996

Spectacle lenses which correct oblique astigmatism at all ocular rotations: investigation of "Merté's' conicoidal surfaces.

Merté (1950) described lens forms that correct oblique astigmatism at all ocular rotations. The front surfaces of all lenses were flat, and the back surfaces were made aspherical as conicoids. Merté did not provide a derivation of his formulae for the appropriate conicoidal surfaces. We show that Merté's formula is correct and describe the nature of appropriate conicoidal back surfaces of spectacle lenses.

Astigmatism↗
PubMed1996

The crossed-cylinder aberroscope: an alternative method of calculation of the aberrations.

The distorted retinal grid image in the cross-cylinder aberroscope is conventionally analysed using a method based upon orthogonal polynomials. This method restricts the amount of data that can be extracted from the grid image and requires the real grid that is placed between the cross-cylinders to be pre-distorted, with the amount of pre-distortion depending upon the vertex distance. We present an alternative method based upon the minimization of least squares that does not have these restrictions and show that it gives essentially the same results as the original orthogonal polynomial method. Furthermore, the minimization of least squares method also provides a measure of 'goodness' of fit (e.g. the minimum of the sum of the squares of the deviations.

Humans↗
PubMed1995

Evidence that aspartic acid 301 is a critical substrate-contact residue in the active site of cytochrome P450 2D6.

Model building studies have intimated a role for aspartic acid 301 in the substrate binding of cytochrome P450 2D6 (CYP2D6). We have tested this hypothesis by generating a range of CYP2D6 mutants substituting a variety of amino acids at this site. The mutant proteins, which included substitution with a negatively charged glutamic acid residue or neutral asparagine, alanine, or glycine residues, were expressed in Saccharomyces cerevisiae. In addition, a mutant where aspartic acid 301 was deleted was also tested. All the mutants expressed approximately equivalent amounts of recombinant apoprotein and, apart from the alanine 301 and the aspartic acid 301 deletion mutants, gave carbon monoxide difference spectra of similar magnitude to the wild type. In the cases of the alanine and deletion mutants, the amount of holoprotein was significantly reduced or absent relative to the amount of apoprotein, indicating restricted heme incorporation. The glutamic acid mutant was shown to have similar catalytic properties to the wild type enzyme toward the substrates debrisoquine and metoprolol; however, some differences in regioselectivity and ligand binding were observed. The mutants containing neutral amino acids at position 301 exhibited marked reductions in catalytic activity. At low substrate concentrations little, if any, activity toward debrisoquine and metoprolol was measured. However, at a higher substrate concentration (2 mM) some activity was observed (about 10-20% of wild type levels). Consistent with the above findings, the debrisoquine-induced spin changes in the mutant proteins were markedly reduced. These data collectively demonstrate that aspartic acid 301 plays an important role in determining the substrate specificity and activity of CYP2D6 and provide experimental evidence supporting the role of this amino acid in forming an electrostatic interaction between the basic nitrogen atom in CYP2D6 substrates and the carboxylate group of aspartic acid 301.

Aspartic Acid↗
PubMed1995

A family of trypanosome cdc2-related protein kinases.

The cyclin-dependent kinases, most notable of which is cdc2, are key regulators of the cell cycle, and are highly conserved in evolution. We have cloned and analysed three cdc2-related kinase-encoding genes (tbcrk1-3) from the protozoan parasite Trypanosoma brucei. tbcrk1 encodes a 34-kDa protein with 54% amino acid (aa) identity to the human cdc2, tbcrk2 a 39-kDa protein with 49% identity and tbcrk3 a 35-kDa protein with 54% identity. tbcrk1-3 have substitutions in the 16-aa sequence, the 'PSTAIRE' domain, that characterises the cdc2-related kinase family, to give PCTAIRE, PSTAVRE and PQTALRE motifs, respectively. The three kinases have conserved Tyr and Thr residues that are sites of phosphorylation in cdc2 and are important for regulating kinase activity. Southern blot analysis revealed that each tbcrk is a single copy gene. Pulse-field electrophoresis located the tbcrk genes to some of the largest of the trypanosome chromosomes at greater than 3 Mb. Western blots with anti-PSTAIRE polyclonal antibody detected proteins of 32, 43 and 65 kDa in all life-cycle stages and a 90-kDa protein in bloodstreams forms, implying the presence of a family of cdc2-related kinases. Trypanosomes have a remarkably large gene family of cdc2-related kinases for such a primitive organism. The crk genes may be involved in controlling aspects of the cell cycle which are linked to the differentiation of the parasite during its complex life cycle.

Amino Acid Sequence↗
PubMed1995

v-Myb DNA binding is required to block thrombocytic differentiation of Myb-Ets-transformed multipotent haematopoietic progenitors.

The E26 avian leukaemia virus encodes a fusion oncoprotein consisting of truncated versions of the c-Myb and c-Ets-1 transcription factors. When used to infect embryonic chicken haematopoietic cells two types of self-renewing progenitors are obtained, namely myeloblasts and 'MEPs' (Myb-Ets progenitors). In earlier work we have shown that myeloblasts transformed by the ts21 mutant of E26, which has a lesion in v-Myb, can be induced to differentiate into macrophages following shift to the non-permissive temperature. Here we show that the ts21 v-Myb is temperature sensitive for DNA binding in band shift experiments and that its inactivation in transformed MEPs induces their maturation into thrombocytes. The MEP transforming capacity of v-Myb is not confined to its fusion with v-Ets, as it is also seen with a virus that co-expresses tsMyb with v-ErbB. As with wild-type E26-transformed MEPs, ts21-transformed MEPs are multipotent, differentiating into eosinophils and myeloblasts following treatment with 12-O-tetradecanoylphorbol-13-acetate. In addition, ts21-transformed myeloblasts differentiate into macrophages when shifted to the non-permissive temperature. This shows that v-Myb blocks haematopoietic differentiation at two distinct stages. In contrast, v-Ets inactivation in MEPs transformed by a ts E26 mutant with a lesion in the corresponding oncoprotein leads to their differentiation into erythrocytes, myeloblasts and probably eosinophils. These data show that the two domains of Myb-Ets selectively affect decision making processes in different types and stages of haematopoietic cells.

Acetyltransferases↗
PubMed1995

Ubiquitin is attached to membranes of baculovirus particles by a novel type of phospholipid anchor.

Purified budded virions of Autographa californica nuclear polyhedrosis virus (AcNPV) contain abundant amounts of free ubiquitin, which has an altered electrophoretic mobility on SDS gels as compared with standard ubiquitin. Phase extraction of virion proteins with Triton X-114 indicated that the modified form of ubiquitin behaved as an integral membrane protein. The membrane-bound form of ubiquitin was labeled with both phosphate and palmitate, and its electrophoretic mobility was altered by treatment with phospholipase A2 and a phosphatidylcholine-specific phospholipase D. Mild trypsin digestion indicated that the acyl group was not linked to the C-terminus of the protein. Acylated ubiquitin could not be radiolabeled with a membrane-impermeable Bolton-Hunter reagent unless virus was pretreated with detergent. Together, these experiments suggest that ubiquitin is attached to the inner face of the viral membrane by a novel type of phospholipid anchor.

Amino Acid Sequence↗
PubMed1995

Mu-opioids activate phospholipase C in SH-SY5Y human neuroblastoma cells via calcium-channel opening.

We have recently reported that, in SH-SY5Y cells, mu-opioid receptor occupancy activates phospholipase C via a pertussis toxin-sensitive G-protein. In the present study we have further characterized the mechanisms involved in this process. Fentanyl (0.1 microM) caused a monophasic increase in inositol 1,4,5-trisphosphate mass formation, with a peak (20.5 +/- 3.6 pmol/mg of protein) at 15 s. Incubation in Ca(2+)-free buffer abolished this response, while Ca2+ replacement 1 min later restored the stimulation of inositol 1,4,5-trisphosphate formation (20.1 +/- 0.6 pmol/mg of protein). In addition, nifedipine (1 nM-0.1 mM), an L-type Ca(2+)-channel antagonist, caused a dose-dependent inhibition of inositol 1,4,5-trisphosphate formation, with an IC50 of 60.3 +/- 1.1 nM. Elevation of endogenous beta/gamma subunits by selective activation of delta-opioid and alpha 2 adrenoceptors failed to stimulate phospholipase C. Fentanyl also caused a dose-dependent (EC50 of 16.2 +/- 1.0 nM), additive enhancement of carbachol-induced inositol 1,4,5-trisphosphate formation. In summary, we have demonstrated that in SH-SY5Y cells activation of the mu-opioid receptor allows Ca2+ influx to activate phospholipase C. However, the possible role of this mechanism in the process of analgesia remains to be elucidated.

Calcium↗
PubMed1995

Dielectric relaxation spectroscopy and some applications in the pharmaceutical sciences.

With a few exceptions, dielectric relaxation spectroscopy (DRS) has been largely neglected by pharmaceutical scientists, despite the potential for this technique as a noninvasive and rapid method for the structural characterization and quality control of pharmaceutical materials. DRS determines both the magnitude and time dependency of electrical polarization (i.e. the separation of localized charge distributions) by either measuring the ability of the material to pass alternating current (frequency domain DRS) or by investigating the current that flows on application of a step voltage (time domain DRS). DRS is thus (i) sensitive to molecular mobility and structure, (ii) non-invasive, and (iii) employs only mild stresses (a weak electromagnetic field) in order to measure the sample properties. The technique covers a broad-band frequency window (from 10(-5) to 10(11) Hz) and therefore enables the investigation of a diverse range of processes, from slow and hindered macromolecular vibrations and restricted charge transfer processes (such as proton conductivity in nearly dry systems) to the relatively fast reorientations of small molecules or side chain groups. The dielectric response provides information on (i) structural characteristics of polymers, gels, proteins, and emulsions, (ii) the interfacial properties of molecular films, (iii) membrane properties, (iv) water content and states of water (and the effects of water as a plasticizer), and (v) lyophilization of biomolecules. This review article details the basis of dielectric theory and the principles of measuring dielectric properties (including a comprehensive account of measurement artifacts), and gives some applications of DRS to the pharmaceutical sciences.

Chemistry, Pharmaceutical↗
PubMed1995

Continuous gradient index and shell models of the human lens.

Because of the complexity of tracing rays through a gradient refractive index medium, the human eye's lens is sometimes approximated by a shell structure with constant refractive index within shells. In the shell model, power arises from a combination of an axial variation in index and the curvatures of the shell surfaces. We develop an equation which gives the power due to the gradient index of the lens, and use this to choose shell models that have the same power as the continuous gradient index model. Some types of shell models are described and evaluated.

Humans↗
PubMed1995

Time series analysis of the prevalence of endoparasitic infections in cats and dogs presented to a veterinary teaching hospital.

The apparent prevalence of endoparasitic infections of cats and dogs presented to the small animal Veterinary Hospital of the University of Pennsylvania was measured between 1984 and 1991. Two thousand feline and 8077 canine fecal samples were examined along with 6830 canine blood samples. The overall mean monthly prevalence of feline infections was 16% for ascarids, 0.9% for hookworms, 4.0% for tapeworms, 2.4% for Giardia spp. and 4.2% for coccidia. The overall mean monthly prevalence of canine infections was 5.7% for ascarids, 9.7% for hookworms, 9.7% for whipworms. 1.8% for tapeworms, 4.7% for Giardia spp. and 3.1% for coccidia. There was a significant downward trend in the prevalence of hookworms and heartworms in dogs (P < 0.001 in both cases). There was a significant upward trend in the prevalence of tapeworms in cats (P < 0.05). There were no significant long-term trends in any of the other time series. The smoothed data were analyzed for seasonal trends. None of the autocorrelation analyses gave incontrovertible evidence of seasonality. The repeated peaks at the 6, 12 and 24 month lags in the case of ascarid infections were suggestive of a 12 month seasonality with a peak prevalence in December, but the results were not statistically significant at the 5% level. Hookworms and whipworms in dogs occurred together more than would be expected by chance in 4 out of the 6 years for which data were available.

Aging↗
PubMed1995

Localization of ornithine decarboxylase (ODC) in the cochlea of the immature rat.

Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis, is important in cochlear development. Whereas tissue specific differences in cochlear ODC activity have been demonstrated, cellular localization of ODC protein in the inner ear of the immature rat has not. ODC was localized in inner ear structures using an ODC polyclonal antibody and the effects of cycloheximide on ODC immunoreactivity and enzymatic activity were determined. Tissues demonstrating elevated enzymatic activity contained cells with the strong immunoreactivity. ODC activity was highest in the organ of Corti and lateral wall followed by the cochlear nerve. Immunoreactivity was demonstrated throughout the cochlea with intense staining of the hair cells, pillar cells, Deiter's cells, inner sulcus cells, basilar membrane, stria vascularis, spiral ganglion cell bodies and cochlear nerve fibers. Cycloheximide rapidly diminished cochlear ODC activity and expression of ODC protein. The half-life of cochlear ODC was 30 min. Localization of cellular sites of ODC is important in understanding the role of the ODC-polyamine pathway in cochlear development and will be a valuable marker for tissue damage from ototoxic agents.

Animals↗
PubMed1995

Determination of GI147211 in human blood by HPLC with fluorescence detection.

GI147211 (GG211) is a camptothecin analogue, which exhibits antileukemic and antitumor activity by blocking DNA synthesis. The drug stability considerations and specimen handling were important aspects in method development and validation. This method involves collection of blood at the clinical site, immediate freezing, and storage at -70 degrees C. The lactone form is extracted from blood at physiological pH with a mixture of n-butyl chloride and acetonitrile (4:1); the carboxylate is not extracted under these conditions. After evaporation the extract is injected into an HPLC system with a fluorescence detector set at 378/420 nm. The internal standard used is 6,7-dimethoxy-4-methylcoumarin. The main advantages of the procedure are the separation of lactone and carboxylate by means of extraction, simplified specimen collection at clinical sites and the ability to inject almost all of the extracted material (extraction recovery, 60%) into an HPLC system. The method has been validated over the range 0.15-100 ng ml-1 with sufficient precision and accuracy (coefficient of variation below 10%) to support pharmacokinetic studies. Under the conditions of this procedure, the drug is stable in human blood at -70 degrees C for at least 93 days, as well as through two additional freeze-thaw cycles.

Antineoplastic Agents↗