Several types of insect cuticle contain enzymes catalyzing the formation ofof adducts between N-acetyldopamine (NADA) and N-acetylhistidine (NAH). Two such adducts, NAH-NADA-I and NAH NADA-II, have been isolated and their structures determined. In one of the adducts the link connecting the two residues occurs between the I-position (ß-position) in the NADA side chain and the 1-N atom (τ-N) in the imidazole ring of histidine. Diphenoloxidase activity alone is not sufficient for formation of this adduct, whereas extracts containing both diphenoloxidase and o-quinone-p-quinone methide isomerase activities catalyze the coupling reaction. The adduct consists of a mixture of two diastereomers and they are presumably formed by spontaneous reaction between enzymatically produced NADA-p-quinone methide and N-acetylhistidine. The other adduct has been identified as a ring addition product of N-acetylhistidine and NADA. In contrast to the former adduct it can be formed by incubation of the two substrates with mushroom tyrosinase alone. An adduct between N-acetylhistidine and the benzodioxan-type NADA-dimer is produced in vitro, when the N-acetylhistidine-NADA adduct is incubated with NADA and locust cuticle containing a 1,2-dehydro-NADA generating enzyme system. Trimeric NADA-polymerization products of the substituted benzodioxan-type have been obtained from in vivo sclerotized locust cuticle, confirming the ability of cuticle to produce NADA-oligomers. The results indicate that some insect cuticles contain enzymes promoting linkage of oxidized NADA to histidine residues. It is suggested that histidine residues in the cuticular proteins can serve as acceptors for oxidized NADA and that further addition of NADA-residues to the phenolic groups of bound NADA can occur, resulting in formation of protein-linked NADA-oligomers. The coupling reactions identified may be an important step in natural cuticular sclerotization.

No description available.

Liposomes incorporating chlorophyll (Chl) have been used as a model system to study various aspects of photosynthesis (such as Chl photooxidation and acceptor reduction). Laser flash photolysis studies of this system have demonstrated that the Chl triplet state (Chl(t)) can transfer an electron to acceptors such as quinones, resulting in the formation of the Chl cation radical (Chl⁺.) and the semiquinone anion radical (Q¯.). Quenching of Chl(t) by quinones in liposomes is diffusion-controlled. The quenching rate is dependent upon bilayer viscosity. Chl(t) lifetimes in the absence of quinones also reflect bilayer viscosity. Radical decay occurs by reverse electron transfer. Although the decay is non-exponential, the decay rate is independent of laser intensity. This is presumably because radical pairs once formed do not become independent of one another and back react in a manner which can be likened to geminate recombination. The non-exponentiality is due to electron exchange between quinone molecules and the heterogeneity in the distribution of molecules among the vesicles. This electron exchange is also manifested in the radical formation process. At high quinone concentration the radical yield increases with quinone concentration in non-linear fashion with respect to the amount of triplet quenched. This positive cooperative effect is interpreted in terms of high quinone concentrations increasing the efficiency of radical production by providing a pathway (via electron hopping) for removal of the electron from the site of initial electron transfer. When ubiquinone is used, only a single fast decay is observed. However, when quinones which can partition between the aqueous and lipid phases are used, radical decay occurs via a fast and a slow process. This is interpreted in terms of electron transfers from Q¯. within the bilayer to Q at the bilayer-water interface which results in a stabilization of the electron transfer products and a slowly-decaying radical. The rate of this slow decay process is also quinone concentration dependent, which is a consequence of a facilitation of electron return to Chl⁺. by Q molecules within the bilayer via an electron hopping mechanism. That such a mechanism is, in fact, operative in radical production is shown also by the observation of electron transfer from UQ¯. to BQ molecules.

Este trabalho apresenta as estruturas determinadas por difração de raio X de dois compostos naftoquinônicos, 3,4-diidro-[2,2-dimetil]-2H-nafto[1,2-b]pirano-5,6-diona (β-lapachona) e dimetil-1,4-naftoquinona. A estrutura cristalina destes compostos mostrou que estes são estabilizados por ligações de hidrogênio do tipo C-H...O, formando estruturas supramoleculares. Dos compostos derivados da β-lapachona, os naftoimidazóis têm-se mostrado muito ativos contra o T. cruzi, agente causador da doença de Chagas. Partindo das estruturas modeladas de 29 compostos naftoimidazólicos, propriedades eletrônicas, geométricas e topológicas foram calculadas para análise estatística por mínimos quadrados parciais (PLS). Após a análise e redução das variáveis foram selecionados os descritores Morp17p, X4a, piPC09, RDF065v, BELp6, RDF060p, R4u, RDF035m e RCI que foram utilizados para a construção um modelo de regressão com o método de PLS. Para o modelo, o menor erro de validação foi obtido com 3 fatores e os coeficientes de correlação R= 0,71 e Q= 0,82. O estudo de docking de alguns compostos naftoquinônicos e naftoimidazólicos mostrou que, do ponto de vista energético e de complementaridade química, estes compostos possuem pouca probabilidade de se ligarem no sítio ativo da tripanotiona redutase (TR), uma enzima essencial para o metabolismo do T. cruzi, bem como no sítio ativo da enzima humana glutationa redutase (GR), homóloga a TR. Há, no entanto, uma tendência geral destes compostos se ligarem no sítio da interface, sobretudo, de se ligarem neste sítio da enzima humana. / This work presents the structure determined by X-ray analyses for two naphthoquinone compounds 3,4-dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6- dione and dimethyl-1,4-naphthoquinone. The crystal packing of these compounds showed the existence of intermolecular hydrogen bonds of the type CH...0. These intermolecular forces are responsible for the self-assembly in three-dimensional supramolecular structure. A set of 29 naphthoimidazoles, derived from β-lapachone, that has shown activity against T. cruzi, the agent of Chagas disease, were modeled. From these structures electronic, geometric, topological, etc, properties were calculated to be used in the investigation by statistic analysis, using the partial least squares method (PLS). After reduction of the number of variables, the best PLS model found was the one obtained with the following variables: Morp17p, X4a, piPC09, RDF065v, BELp6, RDF060p, R4u, RDF035m and RCI. For the PLS model, the lower error of validation was obtained using 3 factors with the coefficients R=0.71 and Q=0.82. Two sets of compounds, naphtoquinones and naphthoimidazoles, were studied by docking method. The results showed that, for both, naphtoquinones and naphthoimidazoles and both trypanothione and glutathione reductase, the compounds have low probability to bind in the active site, and are more likely to bind in the interface site, especially in the interface site of the human protein.

Human hydroxysteroid sulfotransferase (hSULT2A1) catalyzes the sulfation of a broad range of endogenous (e.g., hormones, neurotransmitters, bile acids) as well as xenobiotic (e.g, drugs, environmental pollutants) compounds. Alteration in the catalytic activity of hSULT2A1 can lead to outcomes like endocrine disruptions or aberrant drug metabolism and xenobiotic toxicity. Oxidative and electrophilic stresses are known to cause physiological damage and be implicated as possible underlying pathologic mechanisms of a wide range of diseases. To examine the oxidative as well as electrophilic regulation of hSULT2A1, model oxidants (glutathione disulfide (GSSG), 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), diamide, tert-butyl hydroperoxide (TBHP)) and electrophiles such as quinone metabolites of polychlorinated biphenyls (PCB-quinones) and phenyl-p- benzoquinone were chosen for this study. Mechanistic studies correlating the enzyme structural modifications with alteration in the catalytic properties were performed to elucidate the catalytic regulative mechanism of an individual oxidant or electrophile. Thiol oxidants including GSSG, DTNB, and diamide showed catalytic regulation of hSULT2A1. Changes in protein intrinsic fluorescence indicated conformational alterations in hSULT2A1 following the reaction with diamide. Binding properties of hSULT2A1 for its substrates were also altered after reaction with these thiol oxidants, which could be one major reason for the kinetic alteration due to oxidative modification. Formation of mixed disulfides with cysteines in hSULT2A1 was also identified as a result of reaction with GSSG and DTNB. TBHP was chosen as a model for lipid peroxides, and reaction with this hydroperoxide decreased the catalytic function of hSULT2A1. The dissociation constant for binding of dehydroepiandrosterone (DHEA) was significantly altered with TBHP-pretreatment, but this did not affect the binding of 3',5'-adenosine diphosphate (PAP) to the enzyme. Structural analysis identified cysteine sulfonic acids and methionine sulfoxide formation after reaction of hSULT2A1 with TBHP, which could account for the alterations in the binding properties and the catalytic activity. Both PCB-quinones and PBQ could regulate the catalytic activity of hSULT2A1. Although PCB-quinones only caused decreases in the catalytic activity at all concentrations tested, pretreatment with PBQ indicated that lower concentrations resulted in an increase in the catalytic activity of hSULT2A1 that was followed by a decrease in the catalytic activity of hSULT2A1 upon increasing the concentration of PBQ in the pretreatment. Differences in the dissociation constants of PAP after PBQ-pretreatment were also observed, indicating the key role played by these PCB-quinones in altering the binding of either PAP or the sulfuryl donors, PAPS. Adducts at cysteines in hSULT2A1 were formed following reactions with PCB-quinones and PBQ. Small amounts of cysteine sulfonic acids and methionine sulfoxides were also formed following reaction of the protein with PCB-quinones and PBQ. Therefore, alterations in both the catalytic function as well as the structural properties of hSULT2A1 by interaction with oxidants and electrophiles may lead to changes in the metabolism of xenobiotics, as well as alterations in the endogenous balance of various steroid hormones. Such changes may be an important component in physiological damage that occurs under oxidative and electrophilic stress.

Epidemiological evidence has correlated consumption of sorghum with reduced incidences of gastrointestinal (GI) tract cancer, especially esophageal cancer. There is little evidence on how phenols of sorghum may affect chemoprevention. Seventeen sorghum varieties were screened for phenolic profiles and antioxidant capacity. The ability of crude sorghum extracts to induce NAD(P)H:quinone oxidoreductase (QR, a phase II protective enzyme), and inhibit proliferation of colon (HT-29) and esophageal (OE33) carcinoma cells using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide) and PicoGreen assays, were determined in vitro. 3- Deoxyanthocyanidins, apigeninidin, luteolinidin and their methoxylated derivatives were also investigated for antioxidant capacity, QR inducing and antiproliferative potential. Tannin sorghum generally showed higher antioxidant capacity than non-tannin sorghum varieties. Sorghum varieties containing extractable condensed tannins did not show any significant QR inducing potential; on the other hand, non-tannin sorghums increased QR activity by 1.5-2.7 times; black sorghum (Tx430) was most potent (doubled QR activity at 25 mg/mL, 2.7-fold increase at 100 mg/mL). All sorghum extracts showed relatively strong antiproliferation activity with IC50s (the concentration needed to inhibit cancer cell growth by 50%) of 49.7-883 mg/mL. Tannin-containing sorghums had stronger cancer cell proliferation inhibitory potential (IC50s 49.7-131 mg/mL) than non-tannin sorghums (IC50s 141-883 mg/mL). Total phenol content and antioxidant capacity of crude sorghum extracts positively correlated with their antiproliferative potential (r2 0.71-0.97). Among tested 3-deoxyanthocyanidins, methoxylation on A-ring improved QR inducing potency. 5,7-Dimethoxyluteolinidin had the greatest QR inducing potency (4.3- fold at 100 mM). Methoxylation also improved their antiproliferation potential; the IC50s trend was di-methoxylated (8.3-105 mM) > mono-methoxylated (40.1-192 mM) > apigeninidin and luteolinidin (81.5-284 mM). This study provides information for how phenolic compositions of sorghum and 3-deoxyanthocyanidin structure affect their capacity to induce QR activity and inhibit GI tract cancer cell proliferation. The information is useful to promote the utilization of sorghum in functional foods, beverages, dietary supplements, and other health-related industries. Further study will focus on, fractioned and isolated sorghum phenols, the effect of food processing on their chemopreventive potential, as well as cellular mechanisms involved.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 183-216). Available also in a digital version from Dissertation Abstracts.

No description available.

Thesis (Ph. D.)--University of Nevada, Reno, 2008. / "August, 2008." Includes bibliographical references. Online version available on the World Wide Web.

Thesis (M.Sc. (Chemistry)) - Rhodes University, 2007.