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A study of the mechanism of quercetin oxygenation by 18O labelling. A comparison of the mechanism with that of haem degradation.

ABSTRACT: The mechanism of quercetin oxygenation, which is formally analogous to haem degradation, was studied by using 18O labelling. In both the enzymic oxygenation (catalysed by quercetinase) and the non-enzymic reaction (base-catalysed), both oxygen atoms incorporated into product were derived from a single oxygen molecule. Quercetin oxygenation therefore occurs by a classical dioxygenase mechanism and is not an appropriate model for study of the mechanism of haem catabolism.

SUBMITTER: Brown SB

PROVIDER: S-EPMC1158469 | biostudies-other | 1982 Jul

REPOSITORIES: biostudies-other

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The mechanism of haem catabolism. Bilirubin formation in living rats by [18O]oxygen labelling.

Project description:1. The pathway of haem breakdown in living rats was studied by using 18O in the oxygen that the animals consumed. By cannulation of the common bile duct and collection of bile, labelled bilirubin was isolated and its mass spectrum determined. One set of results was obtained for a rat to which haemoglobin had been intravenously administered and another set obtained for a rat that was not given exogenous haem. Isomerization of bilirubin IXalpha to the XIIIalpha and IIIalpha isomers did not occur to any significant extent. The 18O-labelling pattern obtained in the bilirubin was consistent with a Two-Molecule Mechanism, whereby the terminal lactam oxygen atoms of bilirubin are derived from different oxygen molecules. The consequences of this mechanism are discussed in terms of the possible intermediates of the catabolic pathway. 2. 18O-labelled bilirubin appeared in the bile in less than 10 min after exposure of the animals to labelled oxygen. This result suggests that all of the chemical transformations involving production of biliverdin, reduction to bilirubin and conjugation of the bilirubin are fast processes. 3. The quantitative recovery of label obtained in the experiments suggests that there is little or no exchange of newly synthesized bilirubin with existing bilirubin pools in the animal.

| S-EPMC1183896 | biostudies-other

The mechanism of haem catabolism. A study of haem breakdown in spleen microsomal fraction and in a model system by 18O labelling and metal substitution.

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| S-EPMC1185890 | biostudies-other

An 18O double-labelling study of haemoglobin catabolism in the rat.

Project description:The degradation of haemoglobin to bilirubin in the rat was investigated by 18O labelling of the molecular oxygen consumed by the animal. The oxygen atoms incorporated into bilirubin were derived from two different oxygen molecules. Implications of this finding for the mechanism of haem catabolism in vivo are discussed; both verdohaem and a dioxygen-bridged compound appear to be excluded at intermediates.

| S-EPMC1165773 | biostudies-other

A two-molecule mechanism of haem degradation.

Project description:Coupled oxidation of octaethylhaemin and phenylhydrazine hydrochloride with 16,16O2 and 18,18O2 produced octaethyl[16O]verdohaemochrome and octaethyl[18O]-verdohaemochrome respectively. Reactions of these products with 16,16O2 in the presence of phenylhydrazine hydrochloride yielded octaethyl[16O, 16O]biliverdin and octaethyl[18O, 16O]biliverdin. The same reactions with 18,18O2 yielded octaethyl[16O, 18O]biliverdin and octaethyl[18O, 18O]biliverdin. Accordingly, the two oxygen atoms of biliverdin are incorporated from different O2 molecules in separate reactions, namely the formation of verdohaemochrome and the conversion of verdohaemochrome into biliverdin. These reactions account for a "two-molecule mechanism' of biliverdin formation from haem with verdohaemochrome participating as an intermediate product.

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Stable Isotope Phosphate Labelling of Diverse Metabolites is Enabled by a Family of 18O‐Phosphoramidites**

Project description: Not available

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Quercetin inhibits intestinal non-haem iron absorption by regulating iron metabolism genes in the tissues.

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Uncovering the CO2 Capture Mechanism of NaNO3-Promoted MgO by 18O Isotope Labeling

Project description:MgO-based CO2 sorbents promoted with molten

| S-EPMC9795564 | biostudies-literature

Haem degradation in abnormal haemoglobins.

Project description:The coupled oxidation of certain abnormal haemoglobins leads to different bile-pigment isomer distributions from that of normal haemoglobin. The isomer pattern may be correlated with the structure of the abnormal haemoglobin in the neighbourhood of the haem pocket. This is support for haem degradation by an intramolecular reaction.

| S-EPMC1185868 | biostudies-other

Pharmacokinetic comparison between quercetin and quercetin 3-O-?-glucuronide in rats by UHPLC-MS/MS.

Project description:Quercetin is a natural flavonoid widely distributed in human diet and functional foods. Quercetin 3-O-?-glucuronide (Q3G) is present in wine and some medicinal plants. Quercetin and Q3G may be metabolized from each other in vivo. While quercetin has been the subject of many studies, the pharmacokinetic profiles of quercetin and Q3G (in animals) have not yet been compared. Herein, we prepared a column-based method for rapid isolation of Q3G from Nelumbo nucifera. Then, we developed an UHPLC-MS/MS method to compare the pharmacokinetics of quercetin and Q3G. Our results showed that the plasma concentration-time curves of quercetin and Q3G show two maxima (Tmax1???0.75?h, Tmax2???5?h). After oral administration of 100?mg/kg quercetin or 100?mg/kg Q3G in rats, predominantly Q3G was detected in plasma with AUC at 39529.2?±?6108.2?mg·h·L-1 or 24625.1?±?1563.8?mg·h·L-1, 18-fold higher than quercetin with AUC at 1583.9?±?583.3?mg·h·L-1 or 1394.6?±?868.1?mg·h·L-1, respectively. After intravenous injection of 10?mg/kg in rats, Q3G showed extensive tissue uptake in kidney (409.2?±?118.4?ng/g), liver (166.1?±?52.9?ng/g), heart (97.7?±?22.6?ng/g), and brain (5.8?±?1.2?ng/g). In conclusion, we have shown that Q3G is a major active component in plasma and tissue for oral administration of quercetin or Q3G.

| S-EPMC5075792 | biostudies-literature

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