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D Chapman

Publications and source records attributed to D Chapman.

At least 163 records · Page 9Linked to original sources
PubMed1988

A calorimetric study of the thermotropic behaviour of mixtures of brain cerebrosides with other brain lipids.

We have used a computer-controlled differential scanning calorimeter to determine the phases present in mixtures of the brain galactocerebrosides with other representative brain lipids. There are two types of brain galactocerebroside, those which possess an alpha-hydroxy substituent on the acyl chain (HFA) and those that do not (NFA). In the liquid crystalline state both cerebrosides were miscible with all the lipids studied, but in the gel state they were immiscible with cholesterol and the brain phosphatidylcholines. However, cholesterol mixtures in which the cholesterol mole fraction exceeded one third formed homogeneous metastable gel states on cooling from above the melting point of the cerebroside. Relaxation to the stable two phase state took place slowly over several hours. The solubilities of the galactocerebrosides in the other main brain sphingolipid, sphingomyelin, were much higher. Only in the case of the NFA galactocerebroside and at low mole fractions of sphingomyelin was immiscibility detected. Ternary mixtures of the two cerebrosides with sphingomyelin/cholesterol and phosphatidylcholine/cholesterol (PC/Chol) showed different miscibility characteristics. On cooling from 80 degrees C all mixtures formed homogeneous gel states. However, on standing the cerebrosides separated into discrete gel phases in all mixtures but one, that in which HFA galactocerebrosides were mixed with sphingomyelin and cholesterol. The cerebroside in the mixture with the composition closest to that of myelin, HFA/PC/Chol, melted at 38 degrees C. On scanning guinea pig CNS myelin which had been equilibrated at 5 degrees C a transition was detected with Tmax 33 degrees C. On the basis of comparison with the HFA/PC/Chol mixture we propose that the transition in myelin at this temperature is due to the melting of a galactocerebroside gel phase.

Animals↗
PubMed1988

The bioavailability of Tamoplex (tamoxifen). Part 3. A steady-state study in breast cancer patients.

The bioavailability of two tamoxifen preparations (Tamoplex and Nolvadex) was compared in a multiple dose two-way cross-over design in twelve breast cancer patients. The formulations were found to be bioequivalent. Mean steady-state serum levels of tamoxifen and N-desmethyltamoxifen were 133 ng/ml and 242 ng/ml, respectively, at a single daily dose of three tablets of Tamoplex 10 mg and 128 ng/ml and 248 ng/ml, respectively, at a single daily dose of three tablets of Nolvadex 10 mg. While there was a large interpatient as well as intrapatient variability in steady-state levels of tamoxifen and N-desmethyltamoxifen, their ratio appeared to be constant in the individual patient.

Adult↗
PubMed1988

Nucleotide and deduced amino acid sequence of stp: the bacteriophage T4 anticodon nuclease gene.

Pre-existing host tRNAs are reprocessed during bacteriophage T4 infection of certain Escherichia coli strains. In this pathway, tRNALys is cleaved 5' to the wobble base by anticodon nuclease and is later restored in polynucleotide kinase and RNA ligase reactions. Anticodon nuclease depends on prr, a locus found only in host strains that restrict T4 mutants lacking polynucleotide kinase and RNA ligase; and on stp, the T4 suppressor of prr restriction. stp was cloned and the nucleotide sequences of its wild-type and mutant alleles determined. Their comparison defined an stp open reading frame of 29 codons at 162.8 to 9 kb of T4 DNA (1 kb = 10(3) base-pairs). We suggest that stp encodes a subunit of anticodon nuclease, perhaps one that harbors the catalytic site; while additional subunits, such as a putative prr gene product, impart protein folding environment and tRNA substrate recognition.

Amino Acid Sequence↗
PubMed1988

The properties of brain galactocerebroside monolayers.

Using a Langmuir film balance we have compared the properties of films of the brain galactocerebrosides at 37 degrees C. There are two types of cerebroside in brain, those with an alpha-hydroxy substituent on the acyl chain (HFA) and those without (NFA). At equivalent pressures the areas of both cerebroside films are significantly less than the areas of films of the brain glycerolipids, the choline and ethanolamine phosphatides. The isotherm of NFA galactocerebrosides has two discontinuities, one at low and one at high film pressure, while the isotherm of HFA galactocerebrosides is a smooth curve at all film pressures. Below the high-pressure transition the area of the NFA film is significantly larger than the area of the HFA film. When compressed beyond the high-pressure transition there is a marked hysteresis between compression and expansion isotherms of the NFA galactocerebrosides. The pressures of both films continue to rise steeply when they are compressed into areas which are too small for them to exist as simple monolayers. We conclude that under compression cerebroside films form bilayer structures; that bilayer formation starts at low pressure and occurs progressively as the HFA cerebroside monolayer is compressed, but occurs more abruptly in the NFA cerebroside monolayer at the high-pressure-transition region of the isotherm. A study of pure cerebrosides with a single defined acyl chain shows that there is a correlation between the relative volumes of the hydrophobic and hydrophilic parts of the molecule and the ease of bilayer formation. The larger the relative volume of the hydrophilic group the more readily the cerebroside forms a bilayer film. Other brain lipids added to cerebroside monolayers have sharply differing effects on their areas. The areas of films containing cholesterol are less than the areas calculated by adding the areas of the pure components multiplied by their mole fractions. On the other hand, the area of phosphatidylcholine-containing films is much larger than calculated.

Animals↗
PubMed1988

Models of protein lateral arrangements in lipid bilayer membranes. Application to electron spin resonance studies of cytochrome c oxidase.

We consider the situation of integral membrane proteins in a lipid bilayer matrix where the size of the polar group of the protein is important in determining the lateral packing of the proteins. We represent the cross-section of the protein hydrophobic core as a hexagon moving on a lattice, and represent the projection of the polar group onto the plane of the bilayer as a shape, parts of which overlap the hexagon. Lattice sites represent lipid molecules. We calculate the fraction of lipid molecules which are adjacent to the hydrophobic core of at least one protein. We use this data to consider the "motion restricted" spectrum observed in electron spin resonance (ESR) probe studies, and compute the dependence of the "motion restricted" fraction upon protein concentration. The resulting curves can be used to analyse ESR data in order to deduce the size and shape of the proteins' polar segment. We have used the range of models examined to study the dependence upon protein concentration of the particular case of the "motion restricted" spectrum of a spin-labelled lipid freely diffusing or, alternatively, covalently bound to cytochrome c oxidase. We find that our calculations are in accord with a model where approximately 60 lipid molecules can fit around an isolated such protein in both halves of the bilayer, and where the polar segment is substantially anisotropic and extends laterally beyond the limits of the hydrophobic core. The latter is in accord with what is known about the structure of cytochrome c oxidase. We indicate further measurements that should be performed in order to establish more definitively the dependence of the "motion restricted" component upon protein concentration, giving the lipid protein ratios at which they should be performed, and we make predictions concerning the results. Finally we argue for a particular unified way of plotting experimental data.

Electron Spin Resonance Spectroscopy↗
PubMed1988

Biomembrane structure and function: recent studies and new techniques.

The consensus view of biomembrane structure is outlined. The present model is built upon a fluid lipid matrix, usually two molecules in length, into which the proteins are embedded. The lipid bilayer organization is discussed, such as their phase transition and fluid character and the effect of cholesterol upon the chain organization. The non-lamellar arrangement which some lipids adopt is described. The use of new physical techniques for obtaining information about the structure and dynamics of membrane proteins are described. These techniques include electron diffraction, electron microscopy and FTIR spectroscopy. Models of the structures of the Ca2+-ATPase and the glucose transporter from erythrocytes are shown, indicating the putative helices embedded in the lipid bilayer and the groups of amino acids in the aqueous environment. These models are based upon biochemical methods to obtain amino acid sequences using DNA cloning techniques. Finally, an experimental method using triplet probes is described for the study of the rotational dynamics of membrane proteins. Labelled monoclonal antibodies for studying the dynamics of the glucose transporter have been used.

Animals↗
PubMed1988

A cause-specific hazard rate analysis of prognostic factors among 199 adults with acute lymphoblastic leukemia: the Memorial Hospital experience since 1969.

Results of a multivariable analysis of prognostic factors are reported for 199 previously untreated adults with acute lymphoblastic leukemia (ALL). These patients have long-term follow-up, and the probability of cure is estimated at approximately 35%. The cause-specific hazard rate analysis found lower rates of achieving complete remission (CR) in patients with WBC greater than 10,000/microL, AUL (undifferentiated) morphology, and older age. Since these patients required additional time to respond, fewer of them actually achieved CR. Characteristics directly associated with a higher rate of death during induction therapy due to severe bone marrow suppression were low serum albumin concentration (less than or equal to 3.5 g/dL), age greater than 50 years, acute undifferentiated leukemia (AUL) morphology, low Karnofsky performance status, and weight loss greater than 5%. Factors associated with a higher rate of relapse were WBC greater than 20,000/microL, non-T cell ALL, age greater than 60 years, Ph' + ALL, and time to achieve CR greater than 5 weeks. These criteria were used to identify patients at high risk of relapse. In addition, the predictive value of high WBC was found to disappear by 18 months of continuous CR. Finally, the rate of death following first relapse was higher in patients with a short first remission duration, high percentage weight loss at initial diagnosis, and older age. In summary, factors associated with a higher rate of death during attempted induction (ie, low albumin, high percent weight loss, and poor performance status) had no association with the patient's ability to remain relapse-free. Conversely, factors correlating with more extensive or resistant disease (ie, high WBC, null or B cell ALL, or Ph' + ALL) showed no association with the ability to tolerate therapy. Thus, a less toxic but more effective induction regimen is needed for patients with a poor clinical status, whereas a more intensive form of therapy appears warranted for patients presenting with more extensive or resistant disease.

Adult↗
PubMed1988

Comparison of Healon and Viscoat in cataract extraction and intraocular lens implantation.

Sixty patients were randomly assigned to Healon (20 patients) or Viscoat (40 patients) treatment during extracapsular cataract extraction and intraocular lens implantation surgery. The 40 patients in the Viscoat group were randomly subdivided into two groups. In one group (20 patients), Viscoat was irrigated/aspirated from the eye at the close of surgery, while in the second group of 20 patients, Viscoat was left in the eye. In all Healon cases, the viscoelastic substance was removed from the eye at the end of the surgical procedure. Compared with Viscoat, Healon better facilitated the surgical procedure and appeared to be a more advantageous viscoelastic preparation. Viscoat, in many cases, caused rises in intraocular pressure in the immediate postoperative period when either removed or left in the eye at the close of surgery.

Cataract Extraction↗
PubMed1987

Investigation of the structure and function of the human erythrocyte glucose transporter by proteolytic dissection.

Tryptic and papain digestion have been employed to investigate the structure and function of the human erythrocyte glucose transporter. Trypsin cleaves the native protein into two large, membrane-embedded fragments and a number of small peptides that are released from the membrane. These fragments have been isolated and located within the transporter sequence by fast atom bombardment mass spectrometry and amino acid analysis. The results indicate that the segments of the sequence comprising residues 213-269 and 457-492 are cleaved from the cytoplasmic surface of the membrane by trypsin treatment. These findings are compatible with a model previously proposed for the arrangement of the polypeptide in the membrane (Mueckler, M., et al. (1985) Science 229, 941-945). Despite the loss of these 93 residues, the portion of the protein remaining embedded in the membrane is still able to bind cytochalasin B. This binding is inhibited by D-glucose, indicating that the membrane-embedded fragments retain the substrate-binding site. Fourier transform infrared spectroscopic analysis of the protein before and after proteolytic digestion shows that the intramembranous part of the protein is largely alpha-helical, although some beta-sheet structure appears also to be present. The spectroscopic findings also indicate that the extramembranous, cytoplasmic domain of the transporter, which is removed by trypsin, contains alpha-helical structure.

Amino Acid Sequence↗
PubMed1987

Changes in the secondary structure of apolipoprotein B-100 after Cu2+-catalysed oxidation of human low-density lipoproteins monitored by Fourier transform infrared spectroscopy.

Fourier transform infrared (FTIR) spectra have been obtained of human low-density lipoproteins (LDL) in H2O and 2H2O buffers. The absorption bands are assigned to vibrations of the lipid and apolipoprotein B-100 components. The analysis of second-derivative spectra allowed an assignment of individual protein bands to alpha-helical, random, coil or beta-structure and beta-turn conformations. Changes in the FTIR spectra after Cu2+-catalysed oxidation of the LDL particles indicate that the structure of apolipoprotein B-100 becomes less ordered, with some alterations of alpha-helical and beta-turn conformation. The main beta-structure absorption at 1620 cm-1 is unaffected by oxidation. Taking into account the resistance to oxidation and the slow H-2H exchange it is suggested that the beta-structure is hidden from external factors whereas other structures are mostly present on the surface of the LDL particle. Oxidation affects mainly the surface region of apolipoprotein B-100 and leads to a structural rearrangement which consequently changes the receptor specificity of the LDL.

Apolipoprotein B-100↗
PubMed1987

Conformational changes in concanavalin A associated with demetallization and alpha-methylmannose binding studied by Fourier transform infrared spectroscopy.

Infrared spectra of concanavalin A have been obtained both in the absence and in the presence of the metal ions, Mn2+ and Ca2+, and the saccharide, alpha-methylmannose. Second derivative calculations have been used to determine the frequencies of the different amide I and II components. In the demetallized protein dissolved in H2O buffer, absorptions in the amide I, II and III regions at 1695 and 1634, 1532 and 1237 cm-1, respectively, are assigned to beta-structure, while absorptions at 1563 and both 1318 and 1343 cm-1 are assigned to turns and bends. After deuterium exchange, the residual amide II maximum in the difference spectrum shifts from 1538 to 1563 cm-1, indicating that exchange is faster in the beta-structure than in the turns. In the presence of Mn2+ and Ca2+, the amide II band component at 1532 cm-1 shifts 4-6 cm-1 to higher wavenumbers, and the amide I band component at 1634 shifts 1 cm-1 in the same direction, both in H2O and 2H2O buffers, suggesting changes in the hydrogen-bonding network of a large portion of the protein, particularly in the beta-sheet regions. The addition of alpha-methylmannose increases the magnitude of exchange from 55% to above 90%. Comparison with existing X-ray crystallographic data has been made, and the usefulness of FT-IR to complement this technique is discussed.

Calcium↗
PubMed1987

Forces between proteins and model polypeptides adsorbed on mica surfaces.

The forces of interaction between proteins adsorbed onto mica have been measured as a function of the distance of separation between the two mica surfaces in aqueous solutions. The results for three proteins, myelin basic protein, concanavalin A and cytochrome c, are presented together with the results for a model basic protein, poly(L-lysine). With the exception of cytochrome c at large separations, the forces of interaction are due to charges on the protein surfaces and may be fitted closely to theoretical predictions. For cytochrome c, however, no long-range electrical repulsion is observed, indicating that the negatively charged mica surface has been neutralised by the adsorption of the positively charged protein. At short surface separations, an attraction between the protein surfaces was noted. For concanavalin A, a weak attraction was observed in the presence of calcium and manganese ions only. For poly(L-lysine) and cytochrome c the attraction can be explained simply in terms of van der Waals interactions between the proteins. However, for myelin basic protein the observed attraction was an order of magnitude larger than that predicted by van der Waals theory. We believe that this additional attraction may be due to hydrophobic interactions between the adsorbed myelin basic protein molecules.

Adsorption↗
PubMed1987

Interactions of ovalbumin and of its putative signal sequence with phospholipid monolayers. Possible importance of differing lateral stabilities in protein translocation.

Surface properties of ovalbumin and of its putative signal sequence, and their interactions with phospholipids at an air-water interface, have been studied. The mature protein can form an interfacial film spontaneously from its bulk solution, whereas the signal sequence cannot. Mature ovalbumin also penetrates phospholipid monolayers from the subphase (independently of the type of phospholipid present), whereas its signal sequence does not. The surface stability of a spread film of the signal sequence is, however, higher than that of a film of mature ovalbumin. Above specific threshold concentrations of signal peptide and of mature ovalbumin in mixed films with phospholipids, two separate phases are formed. In such immiscible films, the signal sequence peptide is also able to support a higher lateral surface pressure than mature ovalbumin, at corresponding areas of peptide and mature protein in the mixed monolayers. It is suggested that the differing lateral stabilities of ovalbumin and of its putative signal sequence may be relevant to the translocation of ovalbumin across the membrane of the endoplasmic reticulum, and a scheme for its translocation is proposed that is based on these properties.

Biological Transport↗
PubMed1987

Permeability studies on liposomes formed from polymerizable diacetylenic phospholipids and their potential applications as drug delivery systems.

We have investigated the permeability and entrapment characteristics of liposomes formed from a group of polymerizable phospholipids, containing diacetylenic groups in one or both of their acyl chains. Permeability was assessed by the release of an entrapped dye, 6-carboxyfluorescein. Diacetylenic phosphatidylcholine (PC) liposomes were found to exhibit a wide range of permeability properties, depending on: the nature of the diacetylenic lipid, i.e. mixed-chain (mc) or identical-chain (id), the extent of polymerisation, vesicle size, and cholesterol content. Ultraviolet-initiated polymerisation affected a significant decrease in the permeability of C25idPC liposomes. The increase in permeability of liposomes formed from four other diacetylenic lipids (C25mcPC, C23idPC, C23mcPC and C20idPC) after polymerisation was attributed to disturbances in the packing of lipid molecules, and/or the limited ability of small unilamellar vesicles to accommodate long polymers. The C20idPC lipid is atypical, forming irregular monomeric and polymeric vesicles. The permeability of C25idPC liposomes was also assessed by the release of [3H]inulin. C25idPC liposomes exhibited low permeabilities to [3H]inulin in their monomeric and polymeric states. Incubation of C25idPC liposomes in human plasma caused a substantial increase in the permeability of monomeric vesicles to both carboxyfluorescein and [3H]inulin. The permeability of polymerised C25idPC liposomes, however, was unaffected in the presence of plasma, with vesicles retaining most of their entrapped [3H]inulin after 50 h. These findings demonstrate that polymeric C25idPC liposomes exhibit high resistance to the destructive actions of plasma components, such as high-density lipoproteins (HDLs). Polymeric C25idPC liposomes may have an application in drug delivery systems.

Alkynes↗