Catechol, sulfate conjugation

The major metabolic route for 2-nitrophenol and 4-nitrophenol is conjugation, with the resultant formation of either glucuronide or sulfate conjugates. Conjugates are more polar than the parent compounds and, therefore, are easier to excrete in the urine. Other possible routes of metabolism include reduction to amino compounds or oxidation to dihydric nitrophenols (catechols). In humans, the evidence is indirect and comes from studies of exposure to the pesticide parathion, of which 4-nitrophenol is a metabolite (Fatiadi 1984). 

After re-uptake by the nerve terminal a part of the released dopamine is converted to dihydroxyphenylacetic acid (DOPAC, 5) by intraneuronal monoamine oxidase (MAO) and aldehyde dehydrogenase (AD). Released dopamine is also converted to homovanillic acid (HVA, 6), probably at an extraneuronal site through the sequential action of catechol-O-methyltransferase (COMT) and MAO. In rat brain, DOPAC is the major metabolite and considerable amounts of DOPAC and HVA are present in sulfate-conjugated as well as free forms.1... 

Cytochrome P4502E1, also microsomally located, catalyzes the hydroxylation of phenol to form hydroquinone (and to a much lesser extent catechol), which is then acted upon by the phase II enzymes (Benet et al. 1995 Campbell et al. 1987 Gut et al. 1996 McFadden et al. 1996). All three enzyme systems are found in multiple tissues and there is competition among them not only for phenol but for subsequent oxidative products, like hydroquinone. As a consequence, the relative amount of the products formed can vary based on species, dose and route of administration. In vivo, the gastrointestinal tract, liver, lung, and kidney appear to be the major sites of phenol sulfate and glucuronide conjugation of simple phenols (Cassidy and Houston 1984 Powell et al. 1974 Quebbemann and Anders 1973 ... 

Phenolsulfotransferase catalyzes the transfer of active sulfate from 3 -phosphoadensine 5 -phosphosulfate to various phenols and catechols. Honkasalo and Nissinen (1988) developed an assay that is suitable for measuring both the thermolabile (TL) and thermostable (TS) isoforms of phenol sulfotransferase. Both are active toward phenols, while the TL form also conjugates catechols including dopamine. 

Bromobenzene is excreted as the free and sulfate or mercapturic conjugates of the catechol derivatives. Initially, bromobenzene may concentrate in the adipose tissues. Bromobenzene concentrations can be 300 times higher in the adipose tissues in the first 3 h of exposure. Bromobenzene is rapidly excreted in the urine one report indicated that 85% of the bromobenzene may be excreted in the urine in the first 24 h. 

Glycolate and glyoxylate also plasma and urinary ethylene glycol metabolites Excreted as sulfate and glucuronide conjugates. Other metabolites include catechol and hydroquinone. Urinary phenol excretion not a reliable indicator of benzene exposure. trans,trans-MA and S-phenyl mercapturic acid excretion have been used to assess exposure trans, trans-MA and phenol additional benzene metabolites... 

To be carcinogenic, benzene must first be metabolized in the liver, mainly via cytochrome P4502E1. The major product is phenol (19), which is either conjugated—primarily to phenyl sulfate in humans—or further hydroxylated by P450 2E1 to hydroquinone. Other major metabolites include catechol (34) and trans-trans-mucomc acid (189 1,6-hexadienedioic acid). The latter is presumed to be formed from the ring opening of benzene epoxide (190 benzene oxepin), or perhaps benzene dihydrodiol (191 3,5-cyclohexene-l,2-diol). ... 

The contribution of the gastric mucosa to the metabolism of anthocyanins should not be ruled out because the stomach possesses conjugative enzyme activities (UDP-glucuronosyltransferase, sulfotransferase, and catechol-O-methyl transferase) [47-50]. Besides, in vitro studies showed that some flavonoids could be metabolized into glucuronidated and sulfated metabolites by the gastric wall [45, 51]. 

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