Search results for "Quinone"
showing 10 items of 315 documents
Biocatalytic formation of synthetic melanin: The role of vanadium haloperoxidases, L-DOPA and iodide
2011
The vanadium haloperoxidase (V-HPO) enzyme, extracted from the brown alga Laminaria saccharina, is able to catalyze the formation of a black precipitate, using as precursor the amino acid L-dopa in the presence of hydrogen peroxide and iodide, in one-pot synthesis. The L-dopa oxidation is a multistep reaction with a crucial role played by the iodide in the enzyme catalyzed peroxidative production of dopachrome, a well known intermediate in the synthesis of melanin. Dopachrome is then converted to a synthetic form of melanin through a polymerization reaction. Factors, such as buffer composition and pH, influence significantly the reaction first steps, but further steps of melanin production …
Theileria parasites secrete a prolyl isomerase to maintain host leukocyte transformation
2015
Infectious agents develop intricate mechanisms to interact with host cell pathways and hijack their genetic and epigenetic machinery to change host cell phenotypic states. Among the Apicomplexa phylum of obligate intracellular parasites, which cause veterinary and human diseases, Theileria is the only genus that transforms its mammalian host cells. Theileria infection of bovine leukocytes induces proliferative and invasive phenotypes associated with activated signalling pathways, notably JNK and AP-1 (ref. 2). The transformed phenotypes are reversed by treatment with the theilericidal drug buparvaquone. We used comparative genomics to identify a homologue of the peptidyl-prolyl isomerase PI…
Mitochondrial complex I: new insights from inhibitor assays
2000
The NADH:ubiquinone oxidoreductase (complex I) of the mitochondrial respiratory chain is by far the most complicated of the proton-translocating enzymes involved in the oxidative phosphorylation. Many clues regarding both electron transfer and proton translocation are still unknown. In this sense, inhibitor assays are relevant and useful pieces for elaborating a suitable model to explain the elusive bioenergetic mechanism of this enzyme. This short review presents the most recent advances in inhibitor studies and highlights the major controversies.
EPR, ENDOR and TRIPLE resonance of amino-substituted 9,10-anthraquinone radicals and the rotation of the amino groups in the solution phase
1996
EPR, ENDOR and TRIPLE resonance spectra were recorded for 1-amino-9,10-anthraquinone (1-aminoAQ), 2-aminoAQ, 1,2-diaminoAQ, 1.4-diaminoAQ, 1,5-diaminoAQ and 2,6-diaminoAQ anion radicals in the solution phase. The rotation of the amino groups is discussed with reference to the experimental data. Rotation barrier calculations were carried out using B3PW91/3-21G* density functional method. The amino groups at positions 1, 4, 5, 8 were found not to be in rotational movement up to the EPR time-scale.
Mechanisms of interference of p-diphenols with the Trinder reaction
2020
p-Diphenols, such as homogentisic acid, gentisic acid, etamsylate, and calcium dobesilate, interfere with diagnostic tests utilizing the Trinder reaction but the mechanisms of these effects are not fully understood. We observed substantial differences both in oxidation of p-diphenols by horseradish peroxidase and their influence on oxidation of 4-aminoantipyrine and various phenolic substrates. Homogentisic acid was rapidly oxidized by the enzyme and completely blocked chromophore formation. Enzymatic oxidation of the remaining p-diphenols was slow and they only moderately inhibited chromophore formation. However, in the presence of standard substrates all tested p-diphenols were rapidly co…
Indirect oxidation of amino acid phenylhydrazides by mushroom tyrosinase.
2006
We have investigated oxidation of amino acid phenylhydrazides by mushroom tyrosinase in the presence of 4-tert-butylcatechol and N-acetyl-l-tyrosine. Spectrophotometric measurements showed gradual disappearance of 4-tert-butyl-o-benzoquinone, generated by oxidation of 4-tert-butylcatechol with sodium periodate, after addition of amino acid phenylhydrazides. However, the presence of the phenylhydrazides did not influence the concentration of 4-tert-butyl-o-benzoquinone formed during enzymatic oxidation. Oxygen consumption measurements demonstrated that in a mixture both compounds were oxidized but the reaction rate was proportional to the concentration of the catechol. In the oxidation of N-…
Understanding the influence of lewis acids in the regioselectivity of the diels-alder reactions of 2-methoxy-5-methyl-1,4-benzoquinone: a dft study
2009
The mechanisms of the Diels–Alder (DA) reactions of 2-methoxy-5-methyl-1,4-benzoquinone 1 with 2-methyl-1,3-butadiene 2, in the absence and in the presence of LA catalysts, have been studied using the DFT method at the B3LYP/6-31G(d) level of theory. The uncatalyzed DA reactions between 1 and 2 take place via synchronous concerted TSs. The large activation barrier as well as the low stereo and regioselectivity associated with the uncatalyzed process are in clear agreement with the non-polar character of the cycloaddition. Coordination of the LA catalysts, BF3 or SnCl4, to the oxygen atoms of the benzoquinone 1 produces a large acceleration of the reaction, which can be associated with the l…
Anthraquinones from Ophiorrhiza pumila tissue and cell cultures
1998
We have succeeded in initiating and establishing systems of tissue and cell cultures of Ophiorrhiza pumila. Examination of the constituents of the methanol extract of the cultured calli revealed the presence of 11 anthraquinones including two new ones whose structures have been rigorously proved using advanced spectroscopic methods. These findings demonstrated a remarkable difference in the constituents between the wild plants and the callus tissue or cultured cells; the former is devoid of anthraquinones and contains a variety of camptothecin-related alkaloids whereas the latter contains a significant amount of anthraquinones and shows no indication of the presence of alkaloids after sever…
Shikonin promotes intestinal wound healing in vitro via induction of TGF-β release in IEC-18 cells
2013
The intestinal barrier is a complex system with a dynamic structure that is designed for the maintenance of homeostasis in healthy individuals. Ulcerative colitis, one of the main manifestations of inflammatory bowel disease, is characterized by an inadequate and delayed wound healing. Shikonin, the active principle in the root of Lithospermum erythrorhizon, has demonstrated its ability to attenuate dextran sulfate sodium-induced ulcerative colitis in mice. Moreover, the root of L. erythrorhizon has been used in traditional Chinese medicine for treatment of burns, anal ulcers, hemorrhoids and skin wounds. However, the effect of shikonin on intestinal wound healing is unknown. Using an in vi…
Inhibition of the mutagenicity of 2-nitrofluorene, 3-nitrofluoranthene and 1-nitropyrene by flavonoids, coumarins, quinones and other phenolic compou…
1997
When 56 flavonoids, 32 coumarins, five naphthoquinones, 12 anthraquinones and five structurally-related compounds were tested for their antimutagenic potencies with respect to mutagenicities induced by 2-nitrofluorene (2-NF), 3-nitrofluoranthene (3-NFA) and 1-nitropyrene (1-NP) in Salmonella typhimurium TA98 distinct structure-activity relationships were detected. First, the tetracyclic nitroarenes 3-NFA and 1-NP were in general more effectively antagonized by potent antimutagenic flavonoids and coumarins than the tricyclic 2-NF, while there were only minor differences with quinones. Secondly, antimutagenicity of natural compounds of plant origin correlated with the aglyconic nature 10 of a…