Search PubMed⌕ Search

Biomedical subjects

D Chapman

Publications and source records attributed to D Chapman.

At least 181 records · Page 10Linked to original sources
PubMed1987

The interaction of an anti-lipid antibody (TEPC 15) with a model biomembrane system (monolayer).

The interaction which occurs between an anti-lipid antibody (TEPC 15) and two phospholipids, phosphatidylcholine and phosphatidylethanolamine, when they are arranged in a lipid monolayer system has been studied. It is shown that the antibody is stabilised under the influence of a high lateral pressure when it is mixed with a lipid monolayer and that the behaviour of the antibody depends upon the lipid used. Measurements of the surface pressure and surface potential parameters of the lipid monolayers indicate that the antibody interacts differently with phosphatidylcholine compared with phosphatidylethanolamine. The antibody also exhibits a different interaction when it is pretreated with phosphorylcholine prior to being spread with a phosphatidylcholine monolayer. The interaction of the antibody with phosphatidylcholine-cholesterol monolayers has also been studied.

Antibodies↗
PubMed1987

Fourier transform infrared spectroscopic study of the structure and conformational changes of the human erythrocyte glucose transporter.

Fourier transform infrared spectroscopy has been used to study the secondary structure of the human erythrocyte glucose transporter after purification and reconstitution in erythrocyte lipids. The spectra indicate that the glucose transporter contains, in addition to the predominant alpha-helical structure, an appreciable amount of beta-structure and random coil conformation. A study of the time dependency of H-2H exchange revealed that more than 80% of the polypeptide backbone is readily accessible to the solvent. This result indicates that a portion of the intramembrane-spanning region of the membrane protein is exposed to the solvent, suggesting the existence of an intraprotein aqueous channel. The residual (10-20%) portion of the protein which exchanges slowly includes some alpha-helical structure, probably situated in a hydrophobic environment inside the membrane. The infrared spectra of transporter preparations were also examined after incubation with substrate and substrate analogues. Compared with the spectra recorded under conditions in which the "inward-facing" form predominates, a small but reproducible shift in the bands assigned to alpha-helical and beta-strand structures is observed after incubation with 4,6-O-ethylidene-D-glucose, which largely fixes the transporter in the "outward-facing" conformation. An increase of temperature, which is known to increase the proportion of transporter in the outward-facing conformation, results in a similar shift in this alpha-helical absorption band.

Erythrocyte Membrane↗
PubMed1987

Medical problems of foreign-born adopted children.

Over 8000 foreign-born children, almost all from third-world countries, are adopted by citizens of the United States each year. Most primary care practitioners do not have enough experience to evaluate and manage their problems efficiently. We reviewed the medical care of the foreign-born adoptees followed up in a single pediatric group practice. The 128 children arrived from one of eight countries in Asia or Latin America at ages ranging from 1 month to 10 years; 57% were female. The median duration of follow-up was 20 months. The most common problems identified included deficient immunizations (37%), intestinal parasites (29%), emotional or behavioral problems (22%), skin diseases (16%), estimated age (12%), scabies and/or lice (10%), and congenital anomales (10%). Twenty-one other classes of problems were identified, including developmental delay, lactose intolerance, vision and hearing deficits, and chronic hepatitis B carrier status. At arrival or within one month, 49% of the children had acute infectious diseases, including upper respiratory tract infection, otitis media, rubeola, varicella, and mumps. Nineteen percent of the children underwent surgical procedures ranging from circumcision to cleft lip-palate repair; 46% of these children were never screened for hepatitis B. Fourteen percent were hospitalized at least once, 5% within the first month after arrival. We developed a simple protocol to screen foreign-born adopted children, allowing rapid identification of treatable problems at the least cost and inconvenience to the family. Thirty-six percent of the families made at least one preadoption visit, permitting an explanation of the protocol and potential problems before the child's arrival.

Adoption↗
PubMed1987

Medroxyprogesterone acetate: variation in serum concentrations achieved with three commercially available preparations.

Twenty-nine females with metastatic or locally recurrent carcinoma of the breast were treated orally with 1 g of medroxyprogesterone acetate (MPA) daily. This was used as a second- or third-line treatment. Serum concentration of MPA was measured over a 28-day period. We have demonstrated a significantly greater area-under-the-concentration-time curve, peak, and steady-state MPA concentration for Provera at 100- and 200-mg tablets (Upjohn) than for Farlutal at 500-mg tablets (Farmitalia). Relative bioavailability of preparations should be considered when prescribing or assessing treatment results when MPA is used.

Adult↗
PubMed1987

The effects of temperature on biological membranes and their models.

The physical effects of temperature on biological membranes are reviewed. Our current understanding of membrane structure is based on a model in which proteins are inserted in or are attached to a lipid bilayer structure. The lipid composition varies between cell types. Phospholipid bilayers undergo phase transitions at temperatures which are dependent on chain length and the structure of the headgroup. These factors also affect the miscibility of phospholipid types. Cholesterol orders the phospholipid chains above their phase transition temperature but disorders them below this temperature. Cerebrosides, which are important constituents of the myelin membrane, form metastable states under certain conditions. The activities of membrane-bound enzymes may be affected by the physical state of the lipid bilayer which, in turn, is affected by temperature. The interactions between the lipid and protein components of membranes have been investigated by a variety of techniques.

Animals↗
PubMed1986

A Fourier transform infrared investigation of the structural differences between ribonuclease A and ribonuclease S.

Fourier transform infrared spectroscopy was used to investigate the small conformational differences which exist between ribonuclease A and ribonuclease S in aqueous systems. Deconvolution and derivative methods were used to observe the overlapping components of the amide I and II bands. These proteins give identical spectra in H2O and after complete exchange in 2H2O. However structural differences are revealed by monitoring the rate of 1H-2H exchange by Fourier transform infrared spectroscopy. At equivalent times of exposure in 2H2O buffer ribonuclease S undergoes greater isotopic exchange than ribonuclease A. Thus complete exchange takes place for ribonuclease S but not ribonuclease A after incubation at room temperature for 8 days. Complete 1H-2H exchange of ribonuclease A was achieved by incubation at 62 degrees C for 30 min. The available X-ray data and comparison with the infrared spectra of other soluble proteins was used to assign the components of the amide I and II bands to various secondary structures. In particular, band shifts observed during the later stages of exchange are associated with slowly exchanging residues in beta-strand and alpha-helical regions. The higher rate of exchange for ribonuclease S is associated with a greater conformational flexibility and a more open structure. The results show that it is necessary to be cautious in making band assignments based on exchange methods unless the extent of exchange is known. Furthermore, it is seen that the combination of Fourier transform infrared spectroscopy and hydrogen-deuterium exchange is a powerful technique for revealing small differences in protein secondary structure.

Fourier Analysis↗
PubMed1986

Derivative spectroscopy of tryptophan fluorescence used to study conformational transitions in the (Ca2+ + Mg2+)-adenosine triphosphatase of sarcoplasmic reticulum.

Second and fourth derivatives have been calculated from the fluorescence emission spectra of N-acetyl tryptophanamide in solvents of varying polarity. It is demonstrated that the otherwise featureless fluorescence emission spectrum can be resolved into a series of discrete bands by the use of the derivative technique. These bands appear to have their origins in the transitions of electrons from the first excited singlet state back to the various vibrational levels of the ground state. The shifting of the fluorescence emission maximum to shorter wavelengths upon decreasing the solvent polarity is shown to be due to changes in the relative contributions of each of the bands combined with smaller changes in the band positions. Derivative spectra have also been obtained from the intrinsic tryptophan fluorescence of the (Ca2+ + Mg2+)-adenosine triphosphatase of sarcoplasmic reticulum membranes. A similar pattern of bands is observed to that found in the model system and is consistent with the majority of the tryptophan residues being located in hydrophobic environments. Addition of calcium ions to the protein results in enhancement of the protein fluorescence accompanied by a small and hitherto unseen blue-shift of the spectrum. The mechanistic implications of this finding are discussed in relation to the calcium transport function of the protein.

Animals↗
PubMed1986

The interaction of phosphatidylcholine bilayers with Triton X-100.

The interaction of multilamellar phosphatidylcholine vesicles with the non-ionic detergent Triton X-100 has been studied under equilibrium conditions, specially in the sub-lytic range of surfactant concentrations. Equilibrium was achieved in less than 24 h. Estimations of detergent binding to bilayers, using [3H]Triton X-100, indicate that the amphiphile is incorporated even at very low concentrations (below its critical micellar concentration); a dramatic increase in the amount of bound Triton X-100 occurs at detergent concentrations just below those producing membrane solubilization. Solubilization occurs at phospholipid/detergent molar ratios near 0.65 irrespective of lipid concentration. The perturbation produced by the surfactant in the phospholipid bilayer has been studied by differential scanning calorimetry, NMR and Fourier-transform infrared spectroscopy. At low detergent concentration (lipid/detergent molar ratios above 3), a reduction in 2H-NMR quadrupolar splitting occurs, suggesting a decrease in the static order of the acyl chains; the same effect is detected by Fourier-transform infrared spectroscopy in the form of blue shifts of the methylene stretching vibration bands. Simultaneously, the enthalpy variation of the main phospholipid phase transition is decreased by about a third with respect to its value in the pure lipid/water system. For phospholipid/detergent molar ratios between 3 and 1, the decrease in lipid static order does not proceed any further; rather an increase in fluidity is observed, characterized by a marked decrease in the midpoint transition temperature of the gel-to-fluid phospholipid transition. At the same time an isotropic component is apparent in both 31P-NMR and 2H-NMR spectra, and a new low-temperature endotherm is detected in differential scanning calorimetric traces. When phospholipid and Triton X-100 are present at equimolar ratios some bilayer structure persists, as judged from calorimetric observations, but NMR reveals only one-component isotropic signals. At lipid/detergent molar ratios below unity, the NMR lines become narrower, the main (lamellar) calorimetric endotherm tends to vanish and solubilization occurs.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1986

No phospholipid monolayer-sugar interactions.

Studies by a number of workers using the Langmuir film balance have shown that when carbohydrates, such as sucrose or glycerol, are dissolved in a subphase on which a phospholipid is spread, film expansion occurs (Cadenhead & Demchak, 1969; Cadenhead & Bean, 1972; Maggio et al., 1976; Maggio & Lucy, 1978). Recently such effects have been observed again, particularly with the carbohydrates galactose and trehalose (Johnston et al., 1984). The origin of these film expansions was uncertain, and various suggestions have been made to explain them. One idea was that they might be due to interactions which these carbohydrates have with the water molecules close to the polar head groups of the lipids. Recent studies in our two laboratories, described here, show that the magnitude of the expansion effects is variable and that in general they arise from surfactant impurities in the sugars. These impurities are observed in carbohydrates which are reputedly of high grade; the amount of impurity present can vary from batch to batch, and sometimes they can be difficult to remove. Film balance techniques or subphase preparation can mask the detection of minor impurities. The presence of surfactant impurities in reputedly pure carbohydrates needs to be considered in other biochemical and biophysical studies of lipids and cell membranes.

Carbohydrates↗
PubMed1986

Properties of signal-sequence peptides at an air-water interface.

The surface behaviour of three signal-sequence polypeptides (the pretrypsinogen 2 signal sequence, a synthetic consensus signal sequence and the putative signal sequence of ovalbumin) were studied at an air-water interface. It was found that the surface stabilities of the spread polypeptide films were higher than those of polypeptides and proteins previously investigated (including melittin and membrane proteins), and that the signal peptides had a much lower affinity for the interface than had other peptides and proteins. The observed molecular areas of the signal-sequence peptides indicated that the molecules have a considerable degree of secondary structure at the surface interface.

Adsorption↗
PubMed1986

An infrared spectroscopic study of metastable and stable forms of hydrated cerebroside bilayers.

Fourier transform infrared spectroscopy has been used to study the stable and metastable forms of a range of cerebrosides in aqueous systems. The spectra provide evidence for different degrees of inter- and intra-molecular hydrogen bonding, involving principally the amide group, in these different states. A comparison has been made with the spectra of a cerebroside containing an alpha-hydroxyl group in the fatty acyl chain. This cerebroside does not show metastability and its hydrogen bonding characteristics are shown to be different.

Cerebrosides↗
PubMed1986

Circular dichroism spectra of aqueous dispersions of sphingolipids.

The circular dichroism (CD) spectra of a number of sphingolipids dispersed in water have been studied. The lipids include cerebrosides such as palmitoyl cerebroside, glucocerebroside from the spleen of Gaucher patients, bovine brain galactocerebrosides type I and type II, (BCI and BCII, respectively) and also sphingomyelins such as egg sphingomyelin and bovine brain sphingomyelin. Changes in the CD spectra of the lipids which occur upon heating and cooling and the effects of cholesterol, phosphatidylcholine and the opiate leucine enkephalin were studied.

Animals↗
PubMed1986

Biomembranes as models for polymer surfaces. IV. ESCA analyses of a phosphorylcholine surface covalently bound to hydroxylated substrates.

Using a simple chemical process, phosphorylcholine has been deposited covalently on the surface of a variety of hydroxylated polymers as a stable, monomolecular coating. Our goal was to obtain new biomaterials which, due to the chemical similarity of the modified interfaces to the phospholipid head groups present on the extracellular surfaces of blood cell membranes, should exhibit enhanced haemo- and biocompatibility. Our previous analyses by chemical and spectrophotometric methods indicated that sufficient quantities of phosphorylcholine were deposited on glass and silica surfaces to result in appreciable modification of their interfacial properties. In the present study, we have examined a series of modified hydroxylated substrates by ESCA and demonstrate specific chemical modifications on the molecular surfaces of polymeric substrates.

Chemical Phenomena↗
PubMed1986

Biomembranes as models for polymer surfaces. II. The syntheses of reactive species for covalent coupling of phosphorylcholine to polymer surfaces.

We have proposed previously that the biocompatibility of biomaterial surfaces might be improved by mimicking the phospholipid components which are present on the external faces of cellular plasma membranes. This approach may have particular relevance to the generation of haemocompatible surfaces, since the distributional asymmetry of phospholipids in the plasma membranes of blood cells is critical to the maintenance of haemostasis. The simplest feature common to the external faces of essentially all the mammalian plasma membranes investigated so far is the high content of the electrically neutral, but zwitterionic, phosphorylcholine. The present communication describes the syntheses of a group of novel reactive species capable of covalently linking phosphorylcholine to a variety of polymer surfaces.

Biocompatible Materials↗