103,008 research outputs found
Marriage record of Bugg, Edmond G. and Hackney, Hattie N.
No full textMarriage license for Edmond G. Bugg and Hattie N. Hackney. W.M. McDonald was the officiant
Extradiol oxidative cleavage of catechols by ferrous and ferric complexes of 1,4,7-triazacyclononane: Insight into the mechanism of the extradiol catechol dioxygenases
No full textThe major oxygenation product of catechol by dioxygen in the presence of FeCl2 or FeCl3, 1,4,7-triazacyclononane (TACN), and pyridine in methanol is the extradiol cleavage product 2-hydroxymuconic semi-aldehyde methyl ester (Lin, G.; Reid, G.; Bugg, T. D. I-I. J. Chem. Sec. Chem. Commun. 2000, 1119-1120). Under these conditions, extradiol cleavage of a range of 3- and 4-substituted catechols with electron-donating substituents is observed. The reaction shows a preference in selectivity and rate for iron(II) rather than iron(III) for the extradiol cleavage, which parallels the selectivity of the extradiol dioxygenase family. The reaction also shows a high selectivity for the macrocyclic ligand, TACN, over a range of other nitrogen-and oxygen-containing macrocycles. Reaction of anaerobically prepared iron-TACN complexes with dioxygen gave the same product as monitored by UV/vis spectroscopy. KO2 is able to oxidize catechols with both electron-donating and electron-withdrawing substituents, implying a different mechanism for extradiol. cleavage. Saturation kinetics were observed for catechols, which fit the Michaelis-Menten equation to give k(cat)(app) = 4.8 x 10(-3) s(-1) for 3-(2' ,3'-dihydroxyphenyl)propionic acid. The reaction was also found to proceed using monosodium catecholate in the absence of pyridine, but with different product ratios, giving insight into the acid/base chemistry of extradiol cleavage. In particular, extradiol cleavage in the presence of iron(II) shows a requirement for a proton donor, implying a role for an acidic group in the extradiol dioxygenase active site
Catalytic mechanism of a C-C hydrolase enzyme: Evidence for a gem-diol intermediate, not an acyl enzyme
No full text2-Hydroxy-6-keto-nona-2,4-diene 1,9-dioic acid 5,6-hydrolase (MhpC) from Escherichia coli catalyses the hydrolytic cleavage of the extradiol ring fission product on the phenylpropionate catabolic pathway and is a member of the alpha/beta hydrolase family. The catalytic mechanism of this enzyme has previously been shown to proceed via initial ketonization of the dienol substrate (Henderson, I. M. J., and Bugg,T. D. H. (1997) Biochemistry 36, 12252-12258), followed by stereospecific fragmentation. Despite the implication of an active site serine residue in the alpha/beta hydrolase family, attempts to verify a putative acyl enzyme intermediate by radiochemical trapping methods using a C-14-labeled substrate yielded a stoichiometry of <1% covalent intermediate, which could be accounted for by nonenzymatic processes. In contrast, incorporation of 5-6% of two atoms of O-18 from (H2O)-O-18 into succinic acid was observed using the natural substrate, consistent with the reversible formation of a gem-diol intermediate. Furthermore, time-dependent incorporation of O-18 from (H2O)-O-18 into the carbonyl group of a nonhydrolysable analogue 4-keto-nona-1,9-dioic acid was observed in the presence of MhpC, consistent with enzyme-catalyzed attack of water at the ketone carbonyl. These results favor a catalytic mechanism involving base-catalyzed attack of water, rather than nucleophilic attack of an active site serine. The implication of this work is that the putative active site serine in this enzyme may have an alternative function, for example, as a base
A biomimetic model reaction for the extradiol catechol dioxygenases
No full textA model reaction is described for extradiol catechol cleavage involving FeCl2 or FeCl3, 1,4,9-triazacyclononane (TACN), pyridine and dioxygen which shows similar cofactor and regio-selectivity to the extradiol catechol dioxygenases
Differences in post‐mortem findings after stillbirth in women with and without diabetes
No full textAims: The reason for the fivefold increased risk of stillbirth in women with diabetes is not known. Further understanding of the underlying mechanisms may facilitate identification of pregnancies at increased risk. We have compared post-mortem reports in matched pairs of stillbirths in women with and without diabetes. Methods: Post-mortem reports were provided by the Centre for Maternal and Child Enquiries. Stillbirths as a result of lethal congenital and genetic abnormalities were excluded. Whole body, placenta and organ weights and histo-pathological findings in cases and controls were compared and also related to published reference values. Results: We analysed post-mortem reports on 23 matched pairs of stillbirths from 2009 to 2010. Mean placental weight in women with diabetes was 75 g less than in control subjects (95% CI -143 to -7 g; P = 0.032). In maternal diabetes, the thymus was often small and showed a 'starry sky' pattern on histology in 11 of 20 cases compared with four of 22 controls (P = 0.03). This histological finding was associated with a particularly low mean placental weight z-score -2.1 (1.1) standard deviations below a reference population corrected for gestational age. Conclusions: In over half of the stillbirths occurring in women with diabetes, there was a 'starry sky' appearance in the fetal thymus on histology, this being associated with a small placenta. These findings are consistent with a critical subacute metabolic disturbance being a prominent cause of the increased risk of stillbirth in pregnancies complicated by maternal diabetes.</p
Cis-trans isomerization of a cyclopropyl radical trap catalyzed by extradiol catechol dioxygenases: evidence for a semiquinone intermediate
No full textSubstrate analogues cis- and trans-2-(2,3-dihydroxyphenyl)cyclopropane-1-carboxylic acid were synthesized as probes for a semiquinone radical intermediate in the (2,3-dihydroxyphenyl)propionate 1,2-dioxygenase reaction. These analogues were found to be substrates for oxidative cleavage by extradiol dioxygenases from Escherichia coli and Alcaligenes eutrophus. The stereochemistry of the ring fission products was analyzed by conversion to cyclopropane-1,2-dicarboxylic acids using the ensuing hydrolase enzyme MhpC, followed by GCMS analysis. This analysis revealed 85-94% trans product and 6-15% cis products, implying that cis/trans isomerization of the cyclopropyl ring substituents had taken place during the enzymatic conversion. These results are consistent with a reversible opening of the cyclopropyl ring, and hence consistent with the intermediacy of a semiquinone radical intermediate in the extradiol catechol dioxygenase reaction.</p
Mechanism of extradiol catechol dioxygenases: evidence for a lactone intermediate in the 2,3-dihydroxyphenylpropionate 1,2-dioxygenase reaction
No full textIn lieu of an abstract, this is the article's first paragraph. The oxidative cleavage of catechols by non-heme iron-dependent dioxygenase enzymes is a key step in the bacterial degradation of naturally-occurring and man-made aromatic compounds.1 Two classes of catechol dioxygenases are found: iron(UI)-dependent intradiol dioxygenases, which cleave the carbon—carbon bond between the two hydroxyl groups, and iron(II)-dependent extradiol dioxygenases, which cleave a carbon—carbon bond adjacent to the two hydroxyl groups. Despite extensive spectroscopic studies on these enzymes and the determination of the crystal structure of protocatechuate 3,4-dioxygenase,3 45only limited data are available regarding the mechanism of carbon—carbon bond cleavage. A dioxetane intermediate was originally proposed for the .intradiol enzyme catechol 1,2-dioxygenase based on 1S02 labeling studies; however, more recently an anhydride intermediate has been proposed for the intradiol class, formed by a Criegee rearrangement. In view of the key environmental significance of the catechol dioxygenases and the absence of mechanistic information regarding the extradiol enzymes, we have initiated a study of the mechanism of iron(II)-dependent 2,3-dihydroxyphenyl-propionate 1,2-dioxygenase (MhpB) from Escherichia coli. Here we report evidence from 18G labeling studies and analogue synthesis for a lactone intermediate
2-hydroxy-6-keto-nona-2,4-diene 1,9-dioic acid 5,6-hydrolase: evidence from O-18 isotope exchange for gem-diol intermediate
No full textThe mechanism-based inactivation and subsequent identification of the nucleophilic residue using mass spectrometry have been successfully applied and used to identify the active-site nucleophile in numerous ?-glycosidases, as illustrated using C. fimi exoglycanase. Evidence for a covalent glycosyl-enzyme intermediate has come from X-ray crystallographic analysis of trapped complexes, the first being that of the trapped fluoroglycosyl-enzyme intermediate of Cex. The crystal structure of the trapped fluorocellobiosyl-enzyme complex for Cex has provided useful insights into catalysis and the roles of specific residues at the active site. In addition, information about the conformation of the natural sugar in the covalently bound state and the interactions at the active site was obtained using a mutant form of Cex
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
- …
