Portland State University. Department of Chemistry
Robert M. Strongin
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Chemistry
1 online resource (xvii, 150 pages)
This dissertation focuses on providing quantitative insights regarding kinetic, thermodynamic and mechanistic parameters of neuropeptide S-nitrosylation by nitrous acid (HNO2), peroxynitrite (ONOO-) and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) to produce S-nitrosothiols (SNOs). Peptide thiol stability and the formation of SNOs from neuropeptides; arginine vasopressin (AVP), somatostatin-14 (SST-14) and urotensin II (U-II) was studied. Investigations into the effects of temperature, copper chelators and pH on peptide thiol autoxidation show that AVP, SST-14 and U-II thiols have half-lives of 30, 44 and 28.2 mins respectively at physiologically relevant temperature and pH in the absence of metal chelators. Target peptide thiols were shown to have half-lives sufficient for subsequent S-nitrosylation reactions. The stability of peptide thiol in physiologically relevant conditions suggests novel peptide thiol-mediated chemical signaling mechanisms. We report the formation of S-nitrosothiols: AVP(SNO), SST-14(SNO) and U-II(SNO) through HNO2/NO+ mediated S-nitrosylations. Reported bimolecular rate constants suggest that HNO2 and NO+ would be the predominant nitrosating agents at low pH. Kinetic and EPR analysis implicated copper redox cycling mechanism as catalysts for SNO formation and decomposition. The release of NO during SNO decomposition suggests a potential role for SNOs as efficient NO carrier and donors. Peroxynitrite reactions with peptide thiols showed a complex dependence of acid concentrations with lower bimolecular rates at physiological pH. We present peptide thiols as good candidates for further studies as a peroxynitrite detoxifying compounds. Highly negative activation entropies are reported for SNAP transnitrosation reactions with rate-limiting steps that are characterized by a relatively ordered associative transition state. These activation parameters suggest low energy barriers for transnitrosylation under physiological conditions and support growing evidence that transnitrosylation may be a viable posttranslational mechanism for NO transport in vivo. This dissertation proposes kinetic reaction schemes, thermodynamics and mechanisms related to neuropeptide SNO formation. Researchers can use these insights in the development of potential therapeutics that target endogenous SNOs, and/or utilize synthetic SNOs to stimulate or inhibit NO signaling. Kinetic models presented in this work can be used to infer the NO release profiles of potential NO-donor based drugs by enhancing our understanding of the underlying pharmacokinetics.
© 2021 Vusumuzi Leroy Sibanda
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Sibanda, Vusumuzi Leroy, "Mechanistic Investigation of Neuropeptide S-nitrosylation by Nitric Oxide Moieties: A Kinetic and Thermodynamic Approach" (2021). Dissertations and Theses. Paper 5837.
Available for download on Wednesday, August 17, 2022