Browsing by Author "Onyemata, Ezenwa James"

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    Investigation of the interaction of ceramide and acyl-coenzyme A with the mitochondrial associated protein, endozepine, using heteronuclear NMR
    (University of the Western Cape, 2005) Onyemata, Ezenwa James; Pugh, David J.R.; Dept. of Botany; Faculty of Science
    Endozepine is an alternative name for the testis-specific isoform of the acyl-CoA binding protein (t-ACBP). Acyl-CoA binding proteins form a highly conserved family of proteins, which bind long chain fatty acid esters with nanomolar affinity. They are also known to be endogenous ligands to the --amino butyric acid (GABA) receptor in the central nervous system and to play a role in a wide variety of cellular functions such as vesicular trafficking, fatty acid biosynthesis and gene regulation. A role for endozepine in apoptosis was suggested through promoter gene trapping studies using CHO22 cells in which 90 % reduction in the expression of endozepine correlated with delayed mitochondrial permeabilization, a reduced activation of caspase-3 (an activator of apoptosis) and a consequent resistance to C2-ceramide induced apoptosis. Transduction studies using Tat-GFP-ELP fusion protein showed that endozepine restored the sensitivity of mutant CHO22 cells to C2-ceramide induced apoptosis. In this thesis, we have investigated two hypotheses for the involvement of endozepine in ceramide-induced apoptosis. The first hypothesis is that endozepine contributes to apoptosis through the transport of palmitoyl-CoA, a substrate required for the de novo synthesis of ceramide. The second hypothesis is that endozepine interacts directly with ceramide leading to interaction with peripheral benzodiazepine receptor and a subsequent opening of the mitochondria permeability transition pore, leading to apoptosis.
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    Structural and functional studies of XvPrx2, a type II peroxiredoxin protein from the resurrection plant xerophyta viscosa
    (University of the Western Cape, 2012) Onyemata, Ezenwa James; Pugh, David J.R.; Atkinson, A; Rafudeen, M. S.
    XvPrx2 is a 1-Cys-containing member of the Prx5 subfamily of peroxiredoxins isolated from the resurrection plant Xerophyta viscosa. It is reported to be up-regulated during periods of desiccation and to protect nucleic acids and cellular proteins from oxidative damage through scavenging of reactive oxygen species, suggesting that it may play a role the desiccation tolerance of X. viscosa (Govender, 2006). Members of the Prx5 subfamily have previously been reported to occur as non-covalent homodimers associating across an A-type interface. PrxD from Populus tremula, a close homologue of XvPrx2, forms disulphide bonds with glutathione (glutathionylation) resulting in the unfolding of the Cp-loop and α2-helix and disruption of the homodimer, on the basis of which glutathionylation has been proposed as a physiological mechanism for regeneration of all members of the Prx5 subfamily (Noguera-Mazon, et al., 2006b).