Includes copies of articles co-authored by the author during preparation of this thesis. / Includes bibliographical references (leaves 185-191). / v, 192 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Sixteen aurein peptides are present in the host defence secretion from the granular dorsal glands of the Green and Golden Bell Frog (Litoria aurea) and seventeen from those of the related Southern Bell Frog (Litoria raniformis). All peptides have been sequenced using a combination of electrospray mass spectrometry and Lys-C digestion, with each sequence confirmed by automated Edman sequencing. Ten of these peptides are common to both species of frog. Thirteen of the aurein peptides show wide-spectrum antibiotic and anticancer activity. / Thesis (Ph.D.)--Adelaide University, Dept. of Chemistry, 2001

Benzoquinone (BQ) is an extremely potent electrophilic contact allergen that haptenates endogenous proteins through Michael addition (MA). It is also hypothesized that BQ may haptenate proteins via free radical formation. The objective of this study was to assess the inductive effects (activating and deactivating) of substituents on BQ reactivity and the mechanistic pathway of covalent binding to nucleophilic thiols. The BQ binding by Cys34 on human serum albumin was studied, and for reactivity studies, nitrobenzenethiol (NBT) was used as a surrogate for protein binding of the BQ and benzoquinone derivatives (BQD). Stopped flow techniques were used to determine pseudo-first order rate constants (k) of methyl-, t-butyl-, and chlorine-substituted BQD reactions with NBT, whereas electron pair resonance (EPR) studies were performed to investigate the possible free radical mediated binding mechanism of BQD. Characterization of adducts was performed using mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). The rate constant values demonstrated the chlorine substituted (activated) BQD to be more reactive toward NBT, than the methyl and t-butyl-substituted (deactivated) BQD, and this correlated with the respective EPR intensities. The EPR signal, however, was quenched in the presence of NBT suggesting MA as the dominant reaction pathway. MS and NMR results confirmed adduct formation to be a result of MA of NBT onto the BQ ring with vinylic substitution also occurring for chlorine-substituted derivatives. The binding positions on BQ and NBT/BQD stoichiometric ratios were affected by whether the inductive effects of the substituents on the ring were positive or negative. The reactivity of BQ and BQD is discussed in terms of the potential relationship to allergenic potency. Hammett and Taft (HT) constants were then used to estimate the influence of these substituents on chemical reactivity. HT values demonstrated chlorine substituted BQD to be more reactive than methyl substituted BQD. BQ and BQD dermal allergenicity, as evaluated in the murine local lymph node assay, (LLNA) was consistent with that predicted by reactivity and HT parameters. These results demonstrate the effect of substituents on BQ reactivity and dermal allergic sensitization, and suggest the potential utility of chemical reactivity data and HT values for electrophilic allergen identification and potency ranking.

Most herbicides acting on photosynthetic electron transport are found to be inhibitors that bind to the Q<SUB>B</SUB> protein of photosystem II, which is believed to have a plastoquinone binding site. However, evidence is now available to suggest the existence of other plastoquinone binding sites within the electron-transfer chain of chloroplasts. The cytochrome <i>bf</i> complex is involved in plastoquinol oxidation (QO site) and plastoquinone reduction (QR site). Plastoquinone is also an intermediate in the electron-transfer pathway of ferredoxin-catalysed cyclic photophosphorylation. Recent evidence is available to suggest the existence of a specific ferredoxin-plastoquinone reductase (FQR) which is not associated with the cytochrome <i>bf</i> complex. A series of routine electron-transport assays have been developed to characterize the four plastoquinone-binding sites discussed above. Inhibitors of the QR site inhibited the slow phase of the electrochromic shift (P518<SUB>s</SUB>) and the re-oxidation of cytochrome <i>b</i>-563. QO site inhibitors affected the re-reduction of both cytochromes <i>f</i> and <i>b</i>-563, in addition to the attenuation of P518<SUB>s</SUB>. Cyclic electron transport systems have been set up in broken chloroplasts with either ferredoxin or 9,10-anthraquinone-2-sulphonate as cofactor. FQR inhibitors affected the former cyclic process but not the latter. Evidence was obtained to support the recent notion of the primary site of action of antimycin being at FQR rather than the QR site, which is the primary site in mitochondria. Simple analogues of antimycin such as 3,5 dihalosalicyl-N-(n-substituted) amides also inhibited the FQR. These observations indicated that the inhibitory property of antimycin is associated with the substituted aromatic moiety whilst the remaining dilactone portion provides an additional lipophilicity. The requirement of the aromatic ring for inhibitory activity was confirmed by the effects of tetrahalogenated 4-hydroxy-pyridines. These were found to act not at the QR site as reported in the literature, but at FQR. In addition to the aromatic nucleus, these FQR inhibitors required a phenolic hydroxyl group for activity. Data obtained was consistent with an obligatory, fixed stoichiometry H<SUP>+</SUP>/e<SUP>-</SUP> of three) Q cycle in the cytochrome <i>bf</i> complex, insensitive to antimycin. Kinetic evidence supported the existence of two quinone binding sites in this complex. Inhibition at one of these, QR site, by 2-alkyl quinoline N-oxide required a high degree of lipophilicity as well as the N-oxide and a ring hydroxyl group. Structural features of the inhibitors which appear to distinguish binding at the various sites include the number of redox active groups on the aromatic nucleus, the requirement for an electron withdrawing group ortho to the redox active group, and the requirement for the redox active group to carry a negative charge.

A series of nitrogen derivatives of 1,4-naphthoquinone, which are structurally similar to the compounds of Hall, has been prepared by this worker. In general, the amido groups are those of the long-chain, fatty acids, and it is believed they will have increased physiological activity. These compounds are to be tested for medicinal activity by Parke-Davis and Company.

Graduation date: 1999

No description available.

Thesis (Ph. D.)--Lehigh University, 2001. / Includes bibliographical references and vita.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xvii, 171 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Claudia Turro, Dept.of Chemistry. Includes bibliographical references (p. 168-171).

Cytochrome bc1 (Complex III) is an important enzyme that takes part in the respiratory electron transport chain in vertebrates, yeast, and many bacteria. The complex exists as a dimer, in which each monomer contains three catalytic subunits: cytochrome c1, cytochrome b and the Rieske iron-sulfur protein or ISP. Within the inner mitochondrial membranes of eukaryotes, Complex III catalyzes the transfer of two electrons from ubiquinol (UQH2) to cytochrome c, a water-soluble protein, through a process called the modified Q-cycle mechanism. Under very specific conditions, such as mutations within cytochrome b, disruption of the normal mechanism leads to bypass reactions, including the formation of superoxide and reactive oxygen species. We have sought to restore the activity of a mutant of cytochrome b (T61V) by modifying UQH2, the natural substrate for this enzyme. The structure of the oxidized form, UQ consists of a p-quinone head group and a hydrophobic all-trans polyprenyl unit (tail) that can vary in length, depending on the species in which it is found. The present work highlights modifications to the substituent groups attached to the quinone head and to the all-trans polyprenyl tail. Since the midpoint potentials of these molecules are pH dependent, cyclic voltammetry and spectroelectrochemistry studies in buffered aqueous solutions have been carried out on these molecules (analogs of UQ10). Modifications of the substituent groups attached to the quinone head gave the molecules a different ability to either donate or receive electrons, while modifications to the length of the tail either increased or decreased the solubility of these molecules inside the phospholipid membrane. We examined the normal activity and the production of superoxide in wild-type and (T61V) of bacterial Rhodobacter sphaeroides in the presence of these analogs. We confirmed that to prevent damaging side reactions, normal operation of the Q-cycle requires a fairly narrow window of reduction potentials with respect to the ubiquinol substrate.

No description available.