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dc.contributor.authorLiu, Pingyangen_US
dc.date.accessioned2014-09-20T06:00:07Z
dc.date.available2014-09-20T06:00:07Z
dc.date.issued2013-03-28en_US
dc.identifier.othervt_gsexam:368en_US
dc.identifier.urihttp://hdl.handle.net/10919/50528
dc.description.abstractIn insects, the cuticle provides protection against physical injury and water loss, rigidness for muscle attachment and mechanical support, and flexibility in inter-segmental and joint areas for mobility. As most insects undergo metamorphosis, they need to shred off old cuticle and synthesize new cuticle to fit the body shape and size throughout their life cycles. The newly formed cuticle, mainly composed of cuticular proteins, chitin, and sclerotizing reagents, needs to be hardened through the crosslinks between cuticular proteins and sclerotizing reagents. This dissertation concerns the biochemical activities of several pyridoxal 5-phosphate (PLP)-dependent decarboxylases with most of them involved in insect cuticle hardening. Herein, we first present a detailed overview of topics in reactions and enzymes involved in insect cuticle hardening. Aspartate 1-decarboxylase (ADC) is at the center of this dissertation. beta-alanine, the product of ADC-catalyzed reaction from aspartate, is the component of an important sclerotizing reagent, N-beta-alanyldopamine; the levels of beta-alanine in insects regulate the concentrations of dopamine, therefore affecting insect sclerotization and tanning (collectively referred as cuticle hardening in this dissertation).

Biochemical characterization of insect ADC has revealed that this enzyme has typical mammalian cysteine sulfinic acid decarboxylase (CSADC) activity, able to generate hypotaurine and taurine. The result throws lights on research in the physiological roles of insect ADC and the pathway of insect taurine biosynthesis. Cysteine was found to be  an inactivator of several PLP-dependent decarboxylases, such as ADC, glutamate decarboxylase (GAD) and CSADC. This study helps to understand symptoms associated with the abnormal cysteine concentrations in several neurodegenerative diseases. A mammalian enzyme, glutamate decarboxylase like-1 (GADL1), has been shown to have the same substrate usage as insect ADC does, potentially contributing to the biosynthesis of taurine and/or beta-alanine in mammalian species. Finally, the metabolic engineering work of L-3, 4-dihydroxyphenylalanine decarboxylase (DDC) and 3, 4-dihydroxylphenylacetaldehyde (DHPAA) synthase has revealed that the reactions of these enzymes could be determined by a few conserved residues at their active site. As both enzymes have been implicated in the biosynthesis of sclerotizing reagents, it is of great scientific and practical importance to understand the similarity and difference in their reaction mechanisms. The results of this dissertation provide valuable biochemical information of ADC, DDC, DHPAA synthase, and GADL1, all of which are PLP-dependent decarboxylases. ADC, DDC, DHPAA synthase are important enzymes in insect cuticle hardening by contributing to the biosynthesis of sclerotizing reagents. Knowledge towards understanding of these enzymes will promote the comprehension of insect cuticle hardening and help scientists to search for ideal insecticide targets. The characterization of GADL1 lays groundwork for future research of its potential role in taurine and beta-alanine metabolism.
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dc.format.mediumETDen_US
dc.publisherVirginia Techen_US
dc.rightsThis Item is protected by copyright and/or related rights. Some uses of this Item may be deemed fair and permitted by law even without permission from the rights holder(s), or the rights holder(s) may have licensed the work for use under certain conditions. For other uses you need to obtain permission from the rights holder(s).en_US
dc.subjectaspartate 1-decarboxylase; pyridoxal 5-phosphate; cysteine sulfinic acid; taurine; hypotaurine; beta-alanine; cysteine; glutamaten_US
dc.titleBiochemical studies of enzymes in insect cuticle hardeningen_US
dc.typeDissertationen_US
dc.contributor.departmentBiochemistryen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineBiochemistryen_US
dc.contributor.committeechairLi, Jianyongen_US
dc.contributor.committeememberFinkielstein, Carla V.en_US
dc.contributor.committeememberTu, Zhijianen_US
dc.contributor.committeememberBevan, David R.en_US


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