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K Barnard

Publications and source records attributed to K Barnard.

At least 37 records · Page 2Linked to original sources
PubMed1991

Short and long range order in basement membrane type IV collagen revealed by enzymic and chemical extraction.

Oriented bovine lens capsules give X-ray diffraction patterns suggesting a considerable degree of order in the collagenous components, predominantly type IV collagen. Here we report the effects of preliminary treatment of lens capsules before orientation. Extraction with 4 M guanidinium hydrochloride or with heparinase/hyaluronidase reveals the same collagenous diffraction patterns previously seen after extraction with 1 M NaCl. There is a four-point pattern of d-spacing 3.9 nm, indicating liquid crystal cybotactic nematic organization, along with sharp streaked meridional reflections which index as orders of 21 nm. This suggests that the removal of basement membrane proteoglycans results in a reduction in diffuse scatter and clarification of the pattern. Extraction of the lens capsules with trypsin or dithiothreitol greatly reduces the intensity of the four-point pattern while leaving the meridional pattern unaffected. This strengthens the evidence that the 21 nm period has its origins in the collagen IV helix. Reduction in the four-point pattern could arise if disruption of non-helical NC1 domains or 7S overlap regions allows slippage of the collagen molecules on orientation, weakening the proposed 1 nm intermolecular stagger. Ultra-low angle diffraction patterns of extracted lens capsules show meridional reflections which index as a long-range axial repeat of approximately 95 nm. This is consistent with a model of microfibrils of type IV collagen in which the NC1 domains bind to the collagen helix at approximately 100 nm intervals, as has been previously suggested.

Animals↗
PubMed1989

Molecular organization of type IV collagen: polymer liquid crystal-like aspects.

A new X-ray diffraction pattern from type IV collagen is described, which can be interpreted on the basis of crystalline and liquid crystalline origins of the reflections. Bovine anterior lens capsules extracted with 1 M NaCl and oriented by extension of 60% under constant load gave medium angle X-ray diffraction patterns showing many of the characteristics typical of liquid crystals. Prominent features, apart from those wide angle features attributable to the collagen triple helix, are (1) a four-point pattern of broad reflections at d-spacing 3.9 nm, and layer line spacing near 5 nm. (2) A broad intense equatorial peak centred at 1.24 nm, indicative of liquid-like lateral molecular associations. (3) A set of five sharp, streaked meridional reflections (previously obscured by the broad peak near 5 nm in unextracted capsules). (4) A further six higher angle reflections of a diffuse, arced and broad appearance on the meridian. The sharp streaked meridional reflections emanate from a long-range periodicity of units 8-9 nm in diameter. These features form a self-consistent system if interpreted on the basis of a staggered liquid crystal-like array of collagen molecules, in which case the first five meridionals and remaining broad reflections, sampled on the meridian, can all be indexed as orders of 21 nm.

Collagen↗
PubMed1987

Chemistry of the collagen cross-links. Origin and partial characterization of a putative mature cross-link of collagen.

The conversion of the reducible divalent cross-links in collagen to non-reducible multivalent cross-links in mature collagen has resulted in the identification of several new amino acids as the putative mature cross-link. None of these compounds has completely satisfied the necessary criteria. We have now isolated an amino acid of high Mr, derived from lysine, that is only present in high-Mr peptides derived from mature collagen. Its increase with age of the tissue correlates with the decrease in the reducible cross-links, and it is present both in mature skin and bone, which are initially cross-linked through the aldimine and oxo-imine divalent cross-link respectively. We propose that this amino acid, as yet incompletely characterized and designated compound M, is a major cross-link of mature collagen.

Aging↗
PubMed1987

Basement membrane collagen--evidence for a novel molecular packing.

Type IV collagen is the major structural protein of basement membranes but very little is known about its molecular organisation in vivo. We have used X-ray diffraction of a thick basement membrane, bovine lens capsule, to provide information. Under constant load, lens capsule gave a collagen diffraction pattern of a similar quality to unstretched rat rail tendon. In addition there were clear meridional reflections which indexed as orders of 10 nm, and equatorial reflections at 2.1 and 3.8 nm. These results suggest the ordering of type IV collagen molecules in fibrils, with a 10 nm periodicity along the length of the fibrils.

Animals↗
PubMed1986

Labour relations in health services management.

'Labour relations' or 'industrial relations' refers to employer-employee relations which are both economic as in matters of pay and conditions, and managerial, i.e. the political relationships between management and employees, collectivized through trade unions and professional associations. This paper traces the development of managerial relationships as illustrated by experiences in the British National Health Service particularly over the past 20 years focusing on groups of actors--management (within which may be distinguished government and local managers), health professional workers and other workers--whose interactions need to be studied if managerial relations within health services are to be satisfactorily analysed. We conclude that, although until recently, developments in management have had little impact upon worker behaviour outside unskilled groups, changing economic and other circumstances could create the conditions in which stronger managerial control over professional workers might emerge.

Forecasting↗
PubMed1984

Measurement of anti-glomerular-basement-membrane antibodies by micro ELISA using insoluble antigens.

An enzyme immunoassay, using finely ground rabbit glomerular basement membrane (GBM) as an antigen, was able to detect sheep anti-rabbit GBM antibodies at serum dilutions of 1:32 000. The particulate GBM bound firmly to plastic micro ELISA plates without the aid of a linking agent, and the antigen-coated plates remained stable for several months when stored at -70 degrees C. There were no appreciable differences between amino acid compositions of ground and whole GBM, and no detectable loss of antigens occurred during the grinding procedure. Competitive inhibition assays with collagenase and pepsin digests of rabbit GBM demonstrated preservation of collagenous and non-collagenous antigens in the ground GBM. The assay should prove to be a relatively simple and highly sensitive technique for detecting antibodies to a wide spectrum of GBM antigens.

Amino Acids↗
PubMed1983

Lysozyme is a component of human vascular elastic fibers.

Lysozyme has been demonstrated in the elastic fibers of normal human arteries and veins by the peroxidase-antiperoxidase technique. Preliminary trypsinization of paraffin sections is necessary to unmask the immunoreactive lysozyme.

Animals↗
PubMed1982

Immunoreactive elastin in benign breast tissues. An immunoperoxidase study.

Immunohistological localisation of elastin was achieved by means of the peroxidase-antiperoxidase method after preliminary trypsinisation of sections from 48 benign breast biopsies. The procedure allows retrospective examination of routinely formalin-fixed, paraffin-embedded breast tissue. In general the immunolocalisation of elastin showed a close microanatomical correlation with the fibres demonstrable in sections from the same blocks by standard elastic-fibre stains. Discrepancies between elastic-fibre stains and elastin immunoreactivity appear to relate to the enhanced avidity of the antibody for immature elastin. In this way sites of recent synthesis of elastin were demonstrated in the inner zone of the periductal elastica, sclerosing adenosis, and in the internal elastic lamina of breast arteries which displayed reduplication of the internal elastic lamina or intimal proliferation.

Breast Diseases↗
PubMed1982

Immunological studies with human aortic elastin.

Antibodies to human fetal aortic elastin were isolated from sheep immunized with alpha-elastin peptides. In preliminary tests of specificity using passive hemagglutination, partial cross-reactivity was demonstrated with alpha-elastin from other species. However, in a double antibody radio-immunoassay alpha-elastin peptides from other mammalian species failed to compete with 125I-labelled human alpha elastin. These results suggest the existence of at least two different antigenic sites on the elastin molecule. One, a high affinity site, demonstrates species specificity at low antigen/antibody concentrations. The other, a low affinity site, is common to mammalian elastins and is demonstrated at high antibody/antigen concentrations. In the radioimmunoassay the antibodies showed considerably less avidity for adult human alpha-elastin than for the fetal antigen. This implies that the species specific site is age-dependent and probably involves the cross-linking region of the elastin molecule. Using the sheep antiserum immunohistochemical staining of elastic tissue has been developed. This should prove to be a useful technique for studying polymeric elastin in intact tissue by light microscopy and at the ultrastructural level.

Adult↗
PubMed1982

Some aspects of tissue maturation in fetal and perinatal foals.

Collagen, elastin and structural glycoprotein content of the lungs of 38 fetal and neonatal foals, 8 of which were showing dysmaturity or convulsive syndrome, were measured by standard biochemical means. Glycoprotein content showed little or no change between 100 and 340 days of gestation; elastin remained constant from 100 to about 260 days when there was an exponential increase up to the time of birth, while collagen content rose linearly from 100 days to birth. In dysmature animals there was significantly less collagen in the lungs at birth but the difference in elastin content between the two groups was not statistically significant. There was no clear distinction between glycoprotein content of the dysmature and normal animals. Histological studies indicated that the lung of the fetal horse matures early and in the last third of pregnancy the adult pattern of blood vessels and trabeculae had already appeared. The reduced collagen content in the dysmature foals might be associated with anomalies of collagen synthesis and cross-linking. These could weaken the structure of the lungs and blood vessels and lead to haemorrhages, especially those in the central nervous system, which are a feature of the dysmature syndrome.

Animals↗