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Biomedical subjects

K Roberts

Publications and source records attributed to K Roberts.

At least 181 records · Page 10Linked to original sources
PubMed1983

Variance in resistance to natural and antibody-dependent cellular cytotoxicity and to complement-mediated lysis among K562 lines.

Isolation of sub-populations of the NK-sensitive erythro-leukaemic cell line K562 by limiting dilution techniques has revealed marked clonal variation in susceptibility to natural cytotoxicity. Detailed examination of two such lines (E10/P2 and F9/P2) which differed significantly in their susceptibility to both native and activated NK-cell-mediated lysis revealed that their differences were stable and independent of culture conditions. The resistant (F9/P2) and sensitive (E10/P2) lines had comparable cold-inhibitory and effector-cell adsorption capacities, indicating that differential susceptibility was not attributable to variable expression of NK target structures. F9/P2 was also less susceptible to antibody-dependent cellular cytotoxicity (ADCC) and complement-mediated lysis, indicating the existence of variants with a generalized capacity to resist several immunolytic processes.

Adsorption↗
PubMed1981

High-resolution electron microscopy of glycoproteins: the crystalline cell wall of Lobomonas.

Lobomonas piriformis is a member of an order of green algae (Volvocales) that have crystalline glycoprotein cell walls. As part of a program of investigation of these glycoproteins and their architecture we have studied the cell wall of Lobomonas by a variety of chemical, electron-microscopical and image-analysis techniques. Lobomonas and Vitreochlamys incisa show a very similar structure in their cell walls and represent I of the 4 classes into which all the structures of the wall of these algae that we have so far examined fall. The 2 classes that we have previously studied in detail, represented by Chlamydomonas reinhardii and chlorogonium elongatum, have a crystalline component of the wall that is a more or less smooth continuous surface overlying an amorphous inner wall layer. Although Lobomonas also has this 2-layer structure, the crystalline layer consists of distinct plates, each of which is built around a single, very coherent crystal lattice. The polar nature of the architecture of the cell wall is shown by sectioning and by examination of the cell-wall surface by metal-shadowing of carbon replicas, both of intact cells and of isolated cell-wall plates. There are great similarities in chemical composition between the glycoproteins of the cell wall of C. reinhardii and those of Lobomonas. Both has a large content of hydroxyproline in their amino acid composition and a sugar/hydroxyproline ratio of about 6.0, and both contain sugar sulphates. Lobomonas however has a large glucose content, whereas Chlamydamonas has almost none. Electron micrographs of walls stained with methylamine tungstate and shadowed specimens show that the Lobomonas crystal structure is entirely different from that of C. Reinhardii, and that there is a distinctly different structure in the centre of the plates from that at their edges, although the transition between the 2 areas occurs with no distortion of the crystal lattice. Computer image analysis has been used to calculate reconstructed images of the 2 areas, and by using minimal-dose techniques has yielded 2-dimensional maps of the negatively stained structure at a resolution of I.8 nm. The 2-sided plane group of both areas of the crystal is P2, and the centre area contains 2 distinct structural units, both centered on dyad axes, together with other more complex features. In the edge structure, one of the structural units appears unchanged, but the other unit has a considerably different appearance. The most likely interpretation of this is as a conformational or positional change in one of the subunits. However, because the underlying lattice is so accurately maintained across this transition, it seems probable that the basic structural arrangement that defines the lattice is common to the 2 areas. Some of the computational and mathematical techniques used in the image analysis have not been previously published and are described in detail and compared with published techniques in an Appendix.

Cell Wall↗
PubMed1980

Model for Stress-induced Protein Degradation in Lemna minor.

Transfer of Lemna minor fronds to adverse or stress conditions produces a large increase in the rate of protein degradation. Cycloheximide partially inhibits stress-induced protein degradation and also partially inhibits the protein degradation which occurs in the absence of stress. The increased protein degradation does not appear to be due to an increase in activity of soluble proteolytic enzymes. Biochemical evidence indicates that stress, perhaps acting via hormones, affects the permeability of certain membranes, particularly the tonoplast. A general model for stress-induced protein degradation is presented in which changes in membrane properties allow vacuolar proteolytic enzymes increased access to cytoplasmic proteins.

Journal Article↗
PubMed1979

Febrile seizures.

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Child, Preschool↗
PubMed1978

Water sports.

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Persons with Disabilities↗
PubMed1977

Physical environment and job satisfaction in a community mental health center.

Relocation of professional staff in a community mental health center provided a setting in which to evaluate the effects of physical environment on job satisfaction. Two mental health teams moved from an old, drab central clinic building to new satellite clinics while a third team remained in the old building. Relocated staff reported significant increase in satisfaction with physical surroundings as compared to staff that did not move. Furthermore, satisfaction with physical surroundings had some impact on overall satisfaction ratings. Physical surroundings in a community mental health center may be a mediating variable for staff morale and effectiveness.

Analysis of Variance↗
PubMed1976

The crystalline glycoprotein cell wall of the green alga Chlorogonium elongatum: a structural analysis.

Members of the Chlamydomonaceae, mostly single-celled green algae, have been shown to contain a crystalline glycoprotein cell wall component. Most of the species examined fall into a class of algae whose walls have an identical crystalline unit cell. Chlorogonium elongatum has been chosen as a representative of this class in order to investigate in more detail its cell wall structure. The alga has a spindleshaped cell wall which retains its asymmetric shape on isolation. Sections from walls fized in the presence of tannic acid clearly reveal a regular subunit monolayer, about 20 nm thick, within the wall. Sodium dodecylsulphate (SDS) polyacrylamide gel electrophoresis shows the presence of at least 2 major glycoprotein species in the wall. Negatively stained purified cell walls demonstrate the crystalline nature of the cell wall. Optical diffraction of bright-field images and direct electron diffraction both give clear diffraction patterns whose spacings extend out to 3 nm and fall on a reciprocal lattice whose vectors describe a 2-dimensional unit cell within the wall 21.5 nm X 7.0 nm and an included angle of 80 degrees. Lattice defects within the cell wall are revealed by both negative staining and surface replication. Through-focal series were used to choose images with the optimal degree of underfocus for image processing. Linear integration and optical filtering of such images gave essentially the same result. A similar image was also obtained by computing the autocorrelation function of the amplitudes in the electron-diffraction pattern and the optical-diffraction pattern of the in-focus image. On the basis of these data a 2-dimensional model of the crystalline cell wall layer is presented.

Cell Wall↗