Thesis (M.A.)--University of North Carolina Wilmington, 2009. / Title from PDF title page (January 12, 2010) Includes bibliographical references (p. 111-113)

Thesis (M.A.)--University of North Carolina Wilmington, 2009. / Title from PDF title page (January 11, 2010) Includes bibliographical references (p. 63-68)

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliographical references.

Thesis (M. Sc.)--University of Canterbury, 2006. / Typescript (photocopy). Includes bibliographical references (leaves 61-73). Also available via the World Wide Web.

Mitochondrial and supernatant glutamate-oxalacetate transaminases (EC 2.6.1.1) and supernatant glutamate-pyruvate transaminase (EC 2.6.1.2) were purified 89, 204 and 240-fold respectively, from dolphin muscle. Starch gel electrophoresis of crude and purified perparations revealed that all three enzymes exist as single forms. Km values of a-ketoglutarate, alanine, pyruvate and glutamate for the glutamate-pyruvate transaminase were 0.45, 8.2, 0.87 and 15 mM, respectively. For the glutamate-oxalacetate transaminases, the Km values of a-ketoglutarate, aspartate, oxalacetate and glutamate were 0.76, 0.50, 0.10 and 9.4 mM, respectively, for the mitochondrial form and 0.13, 2.4, 0.06 and 3.2 mM, respectively, for the supernatant form. In all cases, as the assay pH was decreased from pH 7.3, the Km values of the a-keto acids decreased while those of the amino acids increased. This caused the apparent equilibrium constants for the glutamate-oxalacetate transaminases to remain independent of pH. These values were 9.2 and 6.8 for the mitochondrial and supernatant forms, respectively where K'eq = [asPartate][α-ketoglutarate]/[glutamate][oxalacetate]. Studies of the inhibition of the glutamate-oxalacetate transaminases by dicarboxylic acids indicated that these enzymes may be controlled by pools of metabolic intermediates. Three key roles are suggested for the transminases in the energy metabolism of the diving mammal. First, it is believed that a combined action of the transaminases could enhance energy production during hypoxia by providing (1) fumarate from aspartate for the ATP producing reversal of succinate dehydrogenase and (2) α-ketoglutarate from glutamate for the GTP producing succinyl thiokinase reaction. Next, diving mammals probably accumulate more NADH than other mammals during hypoxia. The glutamate-oxalacetate transaminases seem particularly well suited for restoring redox balance via the malate-aspartate cycle after aerobic metabolism is resumed. Finally, since migrating divers oxidize large amounts of stored fats, the combined reactions of the transaminases could be instrumental in providing increased supplies of oxalacetate to condense with the fat derived acetyl CoA in the citrate synthase reaction. / Science, Faculty of / Zoology, Department of / Graduate

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Reproductive senescence in females is a natural part of the aging process. However, the process by which it occurs, and the relative role of each level of the hypothalamic-pituitary-gonadal axis, remains largely unknown. The neural circuitry regulating the hypothalamic axis, including glutamate acting through N-Methyl-D-Aspartate receptors (NMDARs) on GnRH neurons, appears to be key to this process. The NMDAR is tetrameric and composed of an obligatory NR1 subunit together with NR2 subunits. The subunit composition determines the channel kinetics of the receptor and changes through the life span. This dissertation examines the physiological role of the NR2b subunit on LH pulsatile release and LH surge, both important for reproductive function. The expression of NR2b subunits in the anteroventral periventricular (AVPV) nucleus of the hypothalamus was also examined in aging rats. Experiment 1 showed that the NR2b-antagonist, ifenprodil, enhanced pulsatile LH release in estradioltreated females (both age groups). Experiment 2 showed that the LH surge in middle-aged animals was slightly accelerated and that results were dependent upon prior reproductive status of the animals. In Experiment 3, examination of the NR2b-immunoreactive cell population in young, middle-aged, and aged ovariectomized females given vehicle, estradiol, or estradiol with progesterone showed an age-associated decline in NR2b density. However, the immunofluorescent fraction volume of NR1 colocalized with NR2b increased with aging, and that of immunofluorescent fraction volume of NR2b increased with estradiol treatment. This is indicative of the amount of protein expressed in the AVPV. In total, NR2b cell density in the AVPV declines with age, but the amount of NR2b expressed in NR1-positive cells increases, suggesting a larger population of NR2b containing channels. This may translate to age-associated inhibition of GnRH/LH activity, which is relieved with blockade of NR2bcontaining NMDARs. Thus, this dissertation describes a novel way to examine the mechanism by which age-associated changes to neuromodulators of the HPG axis may affect the onset of reproductive senescence. / text