Browsing by Author "Purvis, Langley R"

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    The D-domain of fibrin : structural and functional studies
    (1987) Purves, Maud; Purvis, Langley R; Berman, Mervyn C
    The D-domain of fibrin (ogen) was separated from the parent molecule by plasmin digestion in the presence of calcium and isolated by means of DEAE-anion exchange chromatography followed by gel-filtration in buffer containing 4 M urea. Fluorescent-D-dimer (f-D-dimer) was isolated from a plasmic digest of fibrin clotted in the presence of 2.45 mM dansyl cadaverine, a fluorescent lysine analogue. Fluorescent-D-monomer was a by-product of f-D-dimer purification, the yield being determined by the concentration of dansyl cadaverine. At 2.45 mM f-D-monomer was always present in the digest. The f-D-monomer is probably formed directly and not as a result of degradation of f-D-dimer. The molecule elutes in the fibrinogen-derived-D- monomer position on gel-filtration. A protease was isolated and partially purified from venom of the puffadder (Bitis arietans). Puffadder venom protease is characterized by its ability to cleave D-dimer into symmetrical D-monomers, smaller than plasmin-derived D-monomers from fibrinogen. This characteristic was used to detect the puffadder venom protease activity with fluorescent-D-dimer being used as the substrate. Fractions obtained were assayed for D-dimer cleavage activity and the samples analyzed by means of SDS-PAGE on 4-20% gradient gels under reducing (βME) and non-reducing conditions. The fluorescent bands were located under U.V light and photographed prior to staining with Coomassie Blue. Several methods for the purification of the protease were investigated.
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    The iron-binding proteins of iron-absorbing rat intestinal mucosa
    (1983) Johnson, Glynis; Purvis, Langley R; Jacobs, Peter
    Iron deficiency anaemia is perhaps the most widespread nutritional deficiency disease; as result, the topic of iron absorption has received intensive investigation over a relatively long period of time. Most of the investigative thrust has come from clinical medicine and allied fields, with some associated biochemical investigation. Evidence from the latter has pointed towards the involvement of iron-binding proteins especially ferritin and transferrin in the absorptive process. While the biochemical literature on these two proteins, particularly transferrin, is vast, their roles in iron absorption are obscure. This study was undertaken, therefore, as an investigation into these proteins, their quantitation and role in iron absorption. The physiology of absorption was studied by injection of radiolabelled ferrous ascorbate into isolated intestinal loops and the determination of mucosal, blood and carcass uptake.
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    Metals and the conformation of fibrin
    (1992) Naidoo, Dhesigen P; Purvis, Langley R
    The carboxy terminal of the γ-chain of human fibrinogen contains at least three biologically. important functional domains: (i) the fibrinogen γ-chain polymerisation centre, (ii) the platelet receptor domain and (iii) the site for staphyloccocal clumping. The nature of the site specificity of these interactions necessitates the existence of a preferred conformation for this region, the nature of which has yet to be clearly established. A novel zinc metalloproteinase isolated from puff adder venom (PAV protease) capable of specifically cleaving the di-γ-chain of transglutaminase (Factor XIIIa) catalysed crosslinked plasmin derived D-dimer into apparently symmetrical monomers has been described. The activity is fibrin specific and displays an unusual site specificity for the γ-carboxy terminal domains within the crosslink region. The activity was reported to be potentiated by zinc. The effect of zinc on the digestion of D-dimer by PAV protease was evaluated by SDS-PAGE and by a fluorimetric technique utilising a fluorescent dansylcadaverine conjugate of the substrate (f-D-dimer). A differential zinc binding study determined that the potentiation of activity by zinc was due to a zinc-substrate rather than a zinc-enzyme interaction. The binding constant for zinc to D-dimer was determined by Scatchard analysis of zinc titration data. The interaction of zinc and f-D-dimer was confirmed by fluorescence anisotropy determinations. The nature of the coordination capsule around the metal cation was determined by examining a cobalt-fibrin-D-dimer complex and characterising the difference visible absorption spectrum thereof. The donor ligands from the D-dimer fragment for the metal ion were determined as histidines by examining zinc(II) and cobalt(II) binding to diethylpyrocarbonate modified fibrin-D-dimer and hydroxylamine treated DEPC-fibrin-D-dimer. Through this study it has been established that the PAV protease cleavage of the di-γ-chain of the plasmin derived D-dimer fragment is potentiated by zinc(II) ions through the formation of a novel zinc determined conformation of fibrin-D-dimer. This presents the possibility of a fibrinspecific neo-epitope being manifested in the presence of zinc ions that could provide a means to determine fibrin degradation products more specifically. A model for the neo-epitope has been proposed.