Browsing by Subject "insects"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Extinctions: Past and Present Week 3 - Plant and insect diversification
    (2017-03-17) Chinsamy-Turan, Anusuya; Anderson, John
    In this video, Professor Anusaya Chinsamy-Turan interviews Emeritus Professor John Anderson who reflects on how the End Permian extinction event wrought profound changes in the plant diversity of the time. He discusses specific examples of the change in the kinds of plants present before and after the End Permian event.
  • Thumbnail Image
    Item
    Open Access
    Neutral lipids associated with haemozoin mediate efficient and rapid beta-haematin formation at physiological pH, temperature and ionic composition
    (BioMed Central Ltd, 2012) Ambele, Melvin; Egan, Timothy
    BACKGROUND: The malaria parasite disposes of host-derived ferrihaem (iron(III)protoporphyrin IX, Fe(III)PPIX) by conversion to crystalline haemozoin in close association with neutral lipids. Lipids mediate synthetic haemozoin (beta-haematin) formation very efficiently. However, the effect on reaction rates of concentrations of lipid, Fe(III)PPIX and physiologically relevant ions and biomolecules are unknown. METHODS: Lipid emulsions containing Fe(III)PPIX were prepared in aqueous medium (pH 4.8, 37degreesC) to mediate beta-haematin formation. The reaction was quenched at various times and free Fe(III)PPIX measured colorimetrically as a pyridine complex and the kinetics and yields analysed. Products were also characterized by FTIR, TEM and electron diffraction. Autofluorescence was also used to monitor beta-haematin formation by confocal microscopy. RESULTS: At fixed Fe(III)PPIX concentration, beta-haematin yields remained constant with decreasing lipid concentration until a cut-off ratio was reached whereupon efficiency decreased dramatically. For the haemozoin-associated neutral lipid blend (NLB) and monopalmitoylglycerol (MPG), this occurred below a lipid/Fe(III)PPIX (L/H) ratio of 0.54. Rate constants were found to increase with L/H ratio above the cut-off. At 16 muM MPG, Fe(III)PPIX concentration could be raised until the L/H ratio reached the same ratio before a sudden decline in yield was observed. MPG-mediated beta-haematin formation was relatively insensitive to biologically relevant cations (Na+, K+, Mg2+, Ca2+), or anions (H2PO4, HCO3, ATP, 2,3-diphosphoglycerate, glutathione). Confocal microscopy demonstrated beta-haematin formation occurs in association with the lipid particles. CONCLUSIONS: Kinetics of beta-haematin formation have shown that haemozoin-associated neutral lipids alone are capable of mediating beta-haematin formation at adequate rates under physiologically realistic conditions of ion concentrations to account for haemozoin formation.