Browsing by Author "Bester, A. J."

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Binding of deoxy-thymidine-5'-triphosphate and deoxyadenosine-5'-triphosphate to chrysotile asbestos
    (Academy of Science for South Africa, 2003) Hawtrey, A.; Pieterse, A.; Van Zyl, J. M.; Bester, A. J.; Harington, J. S.
    Tritiated deoxythymidine-5'-triphosphate ([3H]dTTP) and deoxyadenosine- 5'-triphosphate ([3H]dATP) were found to bind strongly to fibres of chrysotile asbestos. Binding of both triphosphates to amosite and crocidolite, however, was much less than that to chrysotile. Further work with chrysotile showed that the binding appears to be electrostatic in nature, with the negative phosphate groups of the nucleotides attaching to the positively charged groups on the mineral fibre. Attachment of the triphosphates to the mineral surface was found to be concentration dependent. Time curves of binding indicated that, for both nucleoside triphosphates, binding was rapid at 20oC and 37oC. Strong binding was also observed at 55oC. Binding at the higher temperatures depended on the type of buffer used and pH. Bound [3H]dTTP and [3H]dATP could be partially removed from chrysotile by 0.1 M sodium pyrophosphate after a short incubation at 20oC. Various chemical reagents that affected binding were studied and are discussed. The possible use of chrysotile asbestos as a solid phase material for the polymerization of dTTP and dATP or activated 5'-phosphorimidazolide of adenosine is also discussed.
  • Thumbnail Image
    Item
    A comparison of stimulation frequency and electro-augmentation on Myocardial function, extensibility, coronary flow rate, oxygen consumption and glucose metabolism
    (Clinics Cardiv Publishing, 2009-02) Brink, A. J.; Bester, A. J.; Lochner, A.; Kotze, J. C. N.
    See full text.
  • Thumbnail Image
    Item
    Conceptual framework for sewer pump problems allowing for fuzzy logic application
    (Water Research Commission, 2015-04) Bester, A. J.; Jacobs, H. E.; Tulleken, J.; Civil Engineering
    Sewer pump station problems in separate sewer systems (separate from stormwater drainage systems) were investigated in order to derive a conceptual framework for decision making. Notwithstanding the fundamental service that efficient sewage pumping provides to a community, it was apparent that limited research has been published on the topic. Research was undertaken to identify, investigate and classify problems at existing operational sewage pump stations by means of site visits, interviews, and an extensive knowledge review. A conceptual framework for sewer pump problems was subsequently derived. The application of the framework is illustrated by means of a fuzzy logic approach to one of the problem classes identified. This study sets the scene for further research into fuzzy-based efficiency indices pertaining to different sewer system components and the ultimate application in sewer system decision support tools.
  • Thumbnail Image
    Item
    Linkage disequilibrium between a marker on the low-density lipoprotein receptor and high cholesterol levels
    (Health & Medical Publishing Group, 1986-07) Brink, P. A.; Steyn, L. T.; Bester, A. J.; Steyn, K.
    We describe the presence of a linkage disequilibrium between high cholesterol levels in Afrikaner individuals and the common allele of the Pvu II restriction fragment polymorphism on the low-density lipoprotein (LDL) receptor gene. The frequencies of the common and the rare allele in a sample of the Afrikaner population were 0,654 and 0,346 (65 individuals) and 0,794 and 0,206 in the hypercholesterolaemic population (34 patients) (P < 0,05). This finding supports other evidence for a founder origin of the high frequency of familial hypercholesterolaemia among Afrikaners.
  • Thumbnail Image
    Item
    Linkage study of the low-density lipoprotein-receptor gene and cholesterol levels in an Afrikaner family : quantitative genetics and identification of a minor founder effect
    (Health & Medical Publishing Group, 1990) Brink, P. A.; Brink, L. T.; Torrington, M.; Bester, A. J.
    Overlap of clinical and biochemical characteristics between hypercholesterolaemia in members of the general population and familial hypercholesterolaemic (FH) individuals may lead to misdiagnosis. Quantitative analyisis of family data may circumvent this problem. A way of looking for an association between plasma cholesterol levels and restriction fragment length polymorphism markers (RFLP) on the low-density lipoprotein (LDL) receptor gene by using reference cholesterol distributions was explored. Linkage, with a logarithm of the odds (LOD) score of 6,8 at θ 0, was detected between cholesterol levels and the LDL receptor in an extended Afrikaner family. Two RFLP-haplotypes, one previously found in a majority of Afrikaner FH homozygotes, and a second, Stu I -, BstE II +, Pvu II +, Nco I +, were associated with high cholesterol levels in this pedigree.
  • Thumbnail Image
    Item
    'n Nuwe metode vir die bepaliog van serotonien in bloed en serebrospinale vloeistof
    (Health & Medical Publishing Group, 1979) Kriek, J. A.; Bester, A. J.; Rossouw, J. J.
    A new rapid method for the microdetermination of serotonin (5-hydroxytryptamine) in plasma and cerebrospinal fluid is described. A recovery coefficient of 98% was obtained in the present method, with the use of [3H]-hydroxytryptamine creatinine sulphate as an internal standard, compared with recovery coefficients of 31% and 66% for the two existing methods generally used for serotonin determination. This method involves a one-step sample deproteinization by perchloric acid, resulting in a high stability of serotonin.